Remove negative scale check

[viirya]

Which issue does this PR close?

Closes #.

Rationale for this change

I re-checked how Spark handles negative scale. Negative scale is not limited to the max scale check.

What changes are included in this PR?

Are there any user-facing changes?

[tustvold]

FWIW C++ arrow does have this check https://github.com/apache/arrow/blob/91ee6dad722ee154d63eea86ce5644e1e658b53b/cpp/src/arrow/util/decimal.cc#L389

But I agree it doesn't really make much sense. We likely need to update some assertion messages / docs as well

[viirya]

I don't find assertion messages referring to negative scale. We only refer max scale in error message while validating scale. So I just update the datatype doc for negative scale.

[tustvold]

I believe this should also update the doc comment on Decimal128Array and Decimal256Array

[ursabot]

Benchmark runs are scheduled for baseline = 9538c26 and contender = 989ab8d. 989ab8d 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