ARROW-15218: [C++] Add decimal support to the indices_nonzero compute function

[c-jamie]

Adds decimal support to the indices_nonzero compute function. This vector function returns the indices of an array that contains values !=0 or !=false.

This can be used in conjunction with existing functions that return a mask to get back the indices where the mask matches.

Have also added a small enhancement to the indices_nonzero tests to use a TYPED_TEST_SUITE for numeric primitives.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-15218

[github-actions]

⚠️ Ticket has not been started in JIRA, please click 'Start Progress'.

[pitrou]

Thanks for this PR! You'll find some comments below.

Also, can you please update the docs in this file?
https://github.com/apache/arrow/blob/master/docs/source/cpp/compute.rst#containment-tests-1

[pitrou]

LGTM. Thank you very much @c-jamie !

[c-jamie]

Amazing - thanks a mill @pitrou for helping me with this.

[ursabot]

Benchmark runs are scheduled for baseline = 09e4a5e and contender = ce0964e. ce0964e is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.36% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.35% ⬆️0.09%] ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java