Use fetch-h2 by default with option to fallback to node-fetch

[andreban]

• node-fetch doesn't support HTTP/2 and has had an issue for
  support open since 2017: Support HTTP/2 node-fetch/node-fetch#342
• fetch-h2 supports HTTP1.1 and HTTP/2 with upgrade.
• Lack of HTTP/2 has been causing issues with developers with server with only HTTP/2 enabled. See Bubblewrap fails on sites that use HTTP/2 #516.
• Changes the code to use fetch-h2 by default, but allows changing the default from FetchUtils.setFetchEngine().

[PEConn]

Great, thanks!

[andreban]

I'm thinking about using node-fetch by default but having a flag that optionally enables fetch-h2. @PEConn WDYT?

[PEConn]

What's the advantage of supporting both node-fetch and fetch-h2? Is it just incase fetch-h2 has some bugs?

[andreban]

Yes. node-fetch has 21 million downloads / week and fetch-h2 around 6k.

[PEConn]

In that case, I suggest we use fetch-h2 by default and allow an option to use node-fetch. That way we'll know if there are any bugs, and if there aren't we can remove node-fetch.

[PEConn]

This is looking good!

Aren't we going to make one of them an optional dependency?

[andreban]

Aren't we going to make one of them an optional dependency?

I don't think there's a big overhead in having both and this allow deciding which one to use when executing the app. Otherwise, users need to decide at install time.

[PEConn]

Gotcha, LGTM