GH-37359: [C#] Add ToList() to Decimal128Array and Decimal256Array

[DanTm99]

Add ToList() methods to Decimal128Array and Decimal256Array.

• Closes: [C#] Add ToList() to Decimal128Array and Decimal256Array #37359

[github-actions]

⚠️ GitHub issue #37359 has been automatically assigned in GitHub to PR creator.

[DanTm99]

@westonpace

[CurtHagenlocher]

@DanTm99 I'm curious whether you find useful to option to specify includeNulls=false. I recognize that it already exists for PrimitiveArray and think that API consistency is a valuable property, but at the same time I wonder about the kind of scenarios where this would be used.

If Decimal128Array and Decimal256Array were to implement IReadOnlyList<decimal?> and ICollection<decimal?> -- allowing efficient use of LINQ ToList() -- would that meet your use case?

[DanTm99]

@CurtHagenlocher yes, the use case I had for this would even be met by Decimal128Array and Decimal256Array just implementing IEnumerable<decimal?>, as all I need to do is use them with LINQ.

The reason I just added these ToList() methods was because it would meet my use case while also making the classes more consistent with PrimitiveArray<T>.

However, implementing IReadOnlyList<decimal?> and ICollection<decimal?> should be done as part of a separate change, as this change was moreso to bring more consistency to this API.

[DanTm99]

@westonpace @CurtHagenlocher Conflict resolved. Ready to review.

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit d357d2d.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.