Add code coverage for OleDragDropHandler.cs file

[Olina-Zhang]

Related #10773

Proposed changes

• Add unit test file: OleDragDropHandlerTests.cs for public methods of the OleDragDropHandler.cs.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.95122%. Comparing base (643f683) to head (10ae4f4).
Report is 7 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                  @@
##                main      #13022          +/-   ##
====================================================
+ Coverage   76.10589%   96.95122%   +20.84533%     
====================================================
  Files           3275        1226        -2049     
  Lines         643803      357225      -286578     
  Branches       47445        5538       -41907     
====================================================
- Hits          489972      346334      -143638     
+ Misses        150266       10049      -140217     
+ Partials        3565         842        -2723     

Flag	Coverage Δ
Debug	96.95122% <100.00000%> (+20.84533%)	⬆️
integration	?
production	?
test	96.95122% <100.00000%> (+0.00078%)	⬆️
unit	?

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[Tanya-Solyanik]

Thank you!