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GH-40788: [C#] Override Accept in MapArray (#40789)

### Rationale for this change

This allows users to implement `IArrowArrayVisitor<MapArray>` and have the `Visit(MapArray)` method called instead of `Visit(ListArray)` or `Visit(IArrowArray)`.

### What changes are included in this PR?

Overrides the `Accept` method to check whether the visitor implements `Visit(MapArray)`, and if not, delegates to the base implementation to handle `IArrowArrayVisitor<ListArray>` or fall back to using an `IArrowArrayVisitor`.

### Are these changes tested?

Yes, I've added unit tests.

### Are there any user-facing changes?

Yes, this is a user-facing change.
* GitHub Issue: #40788

Authored-by: Adam Reeve <adreeve@gmail.com>
Signed-off-by: Curt Hagenlocher <curt@hagenlocher.org>