arrow

GH-37651: [C#] expose ArrowArrayConcatenator.Concatenate (#37652)



### Rationale for this change

New C# drivers need the ability to concatenate arrays, particularly for metadata calls. 

### What changes are included in this PR?

Converts a previously internal class and method to a public class and method. 

### Are these changes tested?

No substantive product changes were made. All tests still pass.

### Are there any user-facing changes?

It exposes previously hidden functionality. 

Resolves https://github.com/apache/arrow/issues/37651 

* Closes: #37651

Lead-authored-by: David Coe <coedavid@umich.edu>
Co-authored-by: davidhcoe <13318837+davidhcoe@users.noreply.github.com>
Signed-off-by: David Li <li.davidm96@gmail.com>