ARROW-13220: [C++] Implement 'choose' function

[lidavidm]

Also makes two changes:

• MakeArrayFromScalar now works with Decimal256 and FixedSizeBinaryType
• VarArgs(min_args=N) for N>1 now works (before different assertions/runtime checks would trigger). Though, might it make sense to update KernelSignature to reflect min_args?

[github-actions]

https://issues.apache.org/jira/browse/ARROW-13220

[lidavidm]

@ursabot please benchmark lang=C++

[ursabot]

Benchmark runs are scheduled for baseline = ca50cd1 and contender = 3c1182c9bdaf656c2ef1c0311e5078f45b87eb78. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Provided benchmark filters do not have any benchmark groups to be executed on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2 (mimalloc)
[Skipped ⚠️ Only ['Python', 'R'] langs are supported on ursa-i9-9960x] ursa-i9-9960x (mimalloc)
[Finished ⬇️0.0% ⬆️0.0%] ursa-thinkcentre-m75q (mimalloc)
Supported benchmarks:
ursa-i9-9960x: langs = Python, R
ursa-thinkcentre-m75q: langs = C++, Java
ec2-t3-xlarge-us-east-2: cloud = True

[lidavidm]

This needs a lot of merge conflict resolving, so moving to draft for now until #10608 is also merged.