Add code coverage for DataGridViewDesigner

[Zheng-Li01]

Related #10773

Proposed changes

Add unit test file: DataGridViewDesignerTests.cs for public methods of the DataGridViewDesigner.cs, except for OnAddColumn and OnEditColumns methods.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.17003%. Comparing base (227fd3b) to head (b278975).
Report is 46 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13014         +/-   ##
===================================================
+ Coverage   76.04966%   76.17003%   +0.12036%     
===================================================
  Files           3269        3276          +7     
  Lines         643544      643891        +347     
  Branches       47429       47446         +17     
===================================================
+ Hits          489413      490452       +1039     
+ Misses        150566      149885        -681     
+ Partials        3565        3554         -11     

Flag	Coverage Δ
Debug	76.17003% <100.00000%> (+0.12036%)	⬆️
integration	18.13486% <ø> (+0.09766%)	⬆️
production	50.27471% <ø> (+0.24329%)	⬆️
test	96.95092% <100.00000%> (+0.01366%)	⬆️
unit	47.60019% <ø> (+0.11296%)	⬆️

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Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[ricardobossan]

Thank you!

[Tanya-Solyanik]

Thank you!