[LANG-1707] Add ArrayUtils.concat methods for concatenating multiple arrays

[ivamly]

Implementation of the LANG-1707 suggestion: added the concat methods to ArrayUtils for convenient concatenation of multiple arrays in a single call.

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[ivamly]

Hi! This is my first contribution to Apache Commons.
I've started by implementing the concat methods for primitive arrays and their corresponding tests.
I would appreciate verification that I'm on the right track. I'm happy to address any feedback and will gladly add the generic T[] method and its tests once the approach is confirmed.

[garydgregory]

Hello @ivamly
I'd like to understand why all this new code is needed? For example, where in Commons components themselves would this be needed?
TY!

[ivamly]

I'm not entirely sure I understand the question correctly. My implementation was based on the Jira ticket and its comments, where adding these methods was discussed and approved (as I understood it).

Could you please clarify what I might be missing? I'd be happy to adjust the approach if needed.