Fix MaskedTextBox PropertyGrid text editor DPI scaling at runtime

[Copilot]

Fixes #14165

Root Cause

The MaskedTextBox text editor dropdown in PropertyGrid uses hardcoded pixel values that don't scale with DPI, causing clipped/undersized rendering at high DPI (e.g., 300%).

Proposed changes

• MaskedTextBoxTextEditorDropDown.cs: Apply LogicalToDeviceUnits() to size and padding values in constructor

  // Before: hardcoded values
  Padding = new Padding(16);
  Size = new Drawing.Size(100, 52);
  
  // After: DPI-aware scaling
  Padding = new Padding(LogicalToDeviceUnits(16));
  Size = LogicalToDeviceUnits(new Drawing.Size(100, 52));

• MaskedTextBoxTextEditorDropDownTests.cs: Add test verifying DPI scaling behavior

Customer Impact

• The MaskedTextBox text editor dropdown list in PropertyGrid uses hard-coded pixel values ​​and displays correctly at different DPI settings.

Regression?

• No

Risk

• Minimal

Screenshots

Before

After

Test methodology

• Manually

Test environment(s)

• .net 10.0.100

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.16401%. Comparing base (05b7c2e) to head (62a08d4).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #14166         +/-   ##
===================================================
+ Coverage   77.15877%   77.16401%   +0.00524%     
===================================================
  Files           3279        3279                 
  Lines         645333      645341          +8     
  Branches       47720       47720                 
===================================================
+ Hits          497931      497971         +40     
+ Misses        143719      143682         -37     
- Partials        3683        3688          +5     

Flag	Coverage Δ
Debug	77.16401% <100.00000%> (+0.00524%)	⬆️
integration	19.00548% <0.00000%> (+0.00138%)	⬆️
production	52.04081% <100.00000%> (+0.01111%)	⬆️
test	97.40565% <100.00000%> (+0.00005%)	⬆️
unit	49.47230% <100.00000%> (+0.02985%)	⬆️

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