Enable DataGridView dark mode theming via AppContext switch

[LeafShi1]

Fixes #14266

Proposed changes

• Introduce an AppContext quirk switch System.Windows.Forms.DataGridViewDarkModeTheming (exposed via LocalAppContextSwitches / AppContextSwitches) to control whether DataGridView uses dark-mode-specific theming, defaulting to enabled for .NET 10 and allowing apps to opt out.
• Add ApplyDarkModeTheming in DataGridView and call it only when dark mode is active and the new switch is enabled, centralizing the dark palette (background, gridlines, header/row colors) for high contrast on dark backgrounds.
• Update DataGridView painting logic for several cell types—core cells, checkbox cells, combo box cells, and column header cells (sort glyphs)—to use adjusted colors and rendering that remain legible and visually correct in dark mode.
• Improve DataGridViewLinkCell in dark mode by using shared LinkUtilities link colors (aligned with LinkLabel’s dark colors) and ensuring selected links render with appropriate selection foreground color for sufficient contrast.
• Keep existing light-mode/legacy behavior unchanged when the AppContext switch is disabled, so existing applications can retain their current appearance without code changes.

Customer Impact

• Users get a DataGridView that automatically renders with readable, high-contrast colors in dark mode by default, while app developers can still opt out via an AppContext switch to preserve existing light-themed behavior if needed.

Regression?

• No

Risk

• Minimal

Screenshots

Before

After

Test methodology

• Manually

Test environment(s)

• 11.0.0-preview.2.26080.101

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

❌ Patch coverage is 4.61538% with 248 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.16791%. Comparing base (9b546b7) to head (dcf698f).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #14267         +/-   ##
===================================================
- Coverage   77.18395%   77.16791%   -0.01604%     
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  Files           3279        3279                 
  Lines         645138      645263        +125     
  Branches       47730       47755         +25     
===================================================
- Hits          497943      497936          -7     
- Misses        143503      143631        +128     
- Partials        3692        3696          +4     

Flag	Coverage Δ
Debug	77.16791% <4.61538%> (-0.01604%)	⬇️
integration	18.98655% <1.92308%> (-0.00409%)	⬇️
production	52.03815% <4.61538%> (-0.02504%)	⬇️
test	97.40479% <ø> (ø)
unit	49.49919% <4.61538%> (-0.00344%)	⬇️

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[Copilot]

Pull request overview

This PR introduces dark mode theming for the DataGridView control via an AppContext switch (System.Windows.Forms.DataGridViewDarkModeTheming), defaulting to enabled for .NET 10+. The changes provide better visual appearance and contrast in dark mode while preserving opt-out capability for backward compatibility.

Changes:

• Added AppContext switch to control DataGridView dark mode theming, with inheritance through style system
• Implemented dark mode rendering for multiple cell types including link cells, combo box cells, checkbox cells, and column header sort glyphs
• Added shared dark mode link colors to LinkUtilities for consistent link rendering across the DataGridView

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 31 comments.

Show a summary per file

File	Description
src/System.Windows.Forms.Primitives/src/System/LocalAppContextSwitches/LocalAppContextSwitches.cs	Added DataGridViewDarkModeTheming switch with .NET 10+ default
src/System.Windows.Forms/System/Windows/Forms/Controls/Labels/LinkUtilities.cs	Added dark mode color constants for links
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewLinkCell.cs	Implemented dark mode link colors with proper selection handling
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewComboBoxCell.DataGridViewComboBoxCellRenderer.cs	Added dark mode rendering for combo box dropdown and readonly buttons
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewColumnHeaderCell.cs	Refactored sort glyph rendering to support solid white glyphs in dark mode
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCheckBoxCell.cs	Switched to CheckBoxRenderer.DrawCheckBoxWithVisualStyles for dark mode support
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCellStyle.cs	Added SortGlyphColor property to allow customization of sort arrow color
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCell.cs	Enhanced GetContrastedColors to provide better contrast in dark mode
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridView.Methods.cs	Added ApplyDarkModeTheming method and integration in OnHandleCreated
src/System.Windows.Forms/PublicAPI.Unshipped.txt	Documented new SortGlyphColor public API