Fix invalid headers of multiple cookie and set-cookie

[chenBright]

What problem does this PR solve?

Issue Number: resolve #2575

Problem Summary:

目前bRPC处理cookie和set-cookie这两个header的逻辑有问题：

1. RFC 9114规定： 多个cookie不能用,分隔，应该要用; ；

If a decompressed field section contains multiple cookie field lines, these MUST be concatenated into a single byte string using the two-byte delimiter of "; " (ASCII 0x3b, 0x20) before being passed into a context other than HTTP/2 or HTTP/3, such as an HTTP/1.1 connection, or a generic HTTP server application.

3. RFC 6265 规定：多个set-cookie不能合并到一个header。

Origin servers SHOULD NOT fold multiple Set-Cookie header fields into
a single header field. The usual mechanism for folding HTTP headers
fields (i.e., as defined in [RFC2616]) might change the semantics of
the Set-Cookie header field because the %x2C (",") character is used
by Set-Cookie in a way that conflicts with such folding.

What is changed and the side effects?

Changed:

1. 多个cookie要用; 分隔；
2. 内部使用std::unordered_multimap代替butil::CaseIgnoredFlatMap，用来支持同时保存多个set-cookie的特性。为了尽量兼容原来的逻辑：
   2.1 GetHeader、SetHeader只对第一个set-cookie生效。当只有一个set-cookie的时候，这两个api的表现不变。
   2.2 AppendHeader会直接创建新的set-cookie。
   2.3 HeaderBegin和HeaderEnd这两个api表现不变，还是可以遍历到所有header。

Side effects:

• Performance effects(性能影响):

• Breaking backward compatibility(向后兼容性):

---

Check List:

• Please make sure your changes are compilable(请确保你的更改可以通过编译).
• When providing us with a new feature, it is best to add related tests(如果你向我们增加一个新的功能, 请添加相关测试).
• Please follow Contributor Covenant Code of Conduct.(请遵循贡献者准则).

[chenBright]

@wwbmmm 有空看看这个PR

[wwbmmm]

这个改动可能会影响性能？有没有和原来的实现做对比

[chenBright]

这个改动可能会影响性能？有没有和原来的实现做对比

unordered_multimap性能肯定比FlatMap性能差。另外，上面通过遍历来获取key对应的所有value的方法也是比较低效的。或许，实现一个multi版本的FlatMap更合适。

[chenBright]

在FlatMap的基础上支持Multi，Multi FlatMap性能跟FlatMap相当，比std::unordered_(multi)map好一些。以下是在本地运行FlatMapTest.perf得到的性能比较：

[ value = 8 bytes ]
Sequentially inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/300/290/2010/210/230
Sequentially erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/1700/150/160/170/250
Sequentially inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 16/15/360/342/206/195/219
Sequentially erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/18/178/159/149/159/149
Sequentially inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/15/415/410/200/192/235
Sequentially erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 14/17/201/181/151/181/154
[ value = 32 bytes ]
Sequentially inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/280/280/250/200/230
Sequentially erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/2070/150/160/160/160
Sequentially inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 17/17/330/329/207/185/212
Sequentially erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/17/172/163/146/157/148
Sequentially inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 17/17/405/406/197/185/215
Sequentially erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/16/206/188/158/168/159
[ value = 128 bytes ]
Sequentially inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/30/290/290/420/220/250
Sequentially erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/180/150/160/160/160
Sequentially inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 22/25/352/349/213/193/222
Sequentially erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/17/170/165/160/171/157
Sequentially inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 21/24/416/422/210/206/242
Sequentially erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 16/16/213/190/163/171/159
[ value = 8 bytes ]
Randomly inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/290/260/250/220/220
Randomly erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/240/220/170/170/180
Randomly inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 16/15/315/309/206/191/215
Randomly erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/17/258/240/155/193/156
Randomly inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/16/378/363/208/191/210
Randomly erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 14/16/311/290/162/187/169
[ value = 32 bytes ]
Randomly inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/280/270/240/230/220
Randomly erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 10/20/250/220/170/180/160
Randomly inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 18/18/310/304/209/192/209
Randomly erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/16/255/247/155/175/152
Randomly inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 17/17/381/367/209/197/214
Randomly erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/17/310/296/163/188/168
[ value = 128 bytes ]
Randomly inserting 100 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 30/40/300/290/280/230/230
Randomly erasing 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/20/230/220/160/180/170
Randomly inserting 1000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 29/33/327/329/219/197/220
Randomly erasing 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 14/16/257/247/159/182/156
Randomly inserting 10000 into FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 35/39/398/400/220/213/246
Randomly erasing 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 35/36/330/319/221/224/200
[ value = 8 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 10/20/140/130/60/70/50
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/172/161/77/54/46
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/16/216/211/73/56/51
[ value = 32 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 10/20/130/130/70/60/50
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/174/163/73/54/49
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/218/217/75/58/52
[ value = 128 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/140/130/80/50/60
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/173/171/73/55/49
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 26/22/238/252/107/89/91
[ value = 8 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/140/130/70/50/60
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/14/180/160/68/57/47
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/221/210/72/57/51
[ value = 32 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 20/10/140/130/70/60/50
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/167/160/69/53/50
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 15/14/224/219/75/59/52
[ value = 128 bytes ]
Seeking 100 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 10/10/140/130/80/50/60
Seeking 1000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 13/13/170/167/70/54/52
Seeking 10000 from FlatMap/MultiFlatMap/std::map/butil::PooledMap/std::unordered_map/std::unordered_multimap/butil::hash_map takes 26/22/238/240/85/70/67

[wwbmmm]

LGTM

[chenBright]

解决与主干的冲突