[11.x] Add test for Arr::sortRecursiveDesc() method.

[lmottasin]

Summary:
This pull request adds a unit test for the Arr::sortRecursiveDesc() method in the Arr utility class. The new test ensures that the method correctly sorts arrays and nested arrays in descending order.

Changes:

• Added a test case in ArrTest to verify the functionality of sortRecursiveDesc().
• The test covers various scenarios including:
  • Sorting simple arrays with numerical and string values.
  • Sorting multi-dimensional arrays with nested elements.
  • Handling of edge cases such as empty arrays and arrays with mixed value types.

Reason:
Adding this test ensures that the sortRecursiveDesc() method behaves as expected across different use cases and improves the robustness of the Arr utility class.

[lmottasin]

@crynobone Review please?