Support decimal negative scale

[viirya]

Which issue does this PR close?

Closes #1785.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[tustvold]

I think we probably want to do a quick parse over the codebase for places that assume the scale is unsigned.

Doing a search for scale as shows a couple of scale as usize which are likely incorrect

[tustvold]

I wasn't sure about this, as the rationale for enforcing the upper limit is if the positive scale exceeds the precision it would result in truncation. I'm not sure this applies to the negative direction. However, the C++ version has this same check, so 🤷 - https://github.com/apache/arrow/blob/91ee6dad722ee154d63eea86ce5644e1e658b53b/cpp/src/arrow/util/decimal.cc#L389

[viirya]

I think we probably want to do a quick parse over the codebase for places that assume the scale is unsigned.

Doing a search for scale as shows a couple of scale as usize which are likely incorrect

These scale as usize in format_decimal_str should be safe as negative case is handled in advance.

Other scale as usages include some in csv reader (scale as u8 and scale as u32), and the scale is from parsing. I think it is safe because we cannot parse a negative scale.

Another two is scale as i32 in ipc when passing i8 scale to i32 into ipc DecimalBuilder. This should be safe too.

The problematic one is to convert scale to u32 in cast_integer_to_decimal. I'm fixing it and will add one test.

[liukun4515]

when I first meet the negative scale, I was confused by this.

[ursabot]

Benchmark runs are scheduled for baseline = 6c466af and contender = 78ab0ef. 78ab0ef is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java