[Preview7/Release] Backport 13747 DarkMode: SystemControlButton rendering

[KlausLoeffelmann]

Fixes System Control Button rendering issues in dark mode, where a control button is either rendering not in dark mode, or has rendering artefacts when rendering in the context of the property grid.

These issues have been pointed out by customers, and are, among others, one of the blockers for GitHub Extensions, which are emotionally discussed on their GitHub issues

gitextensions/gitextensions#9191 (comment)

(and also might even save lives gitextensions/gitextensions#11904)

Note while the latter is certainly an ironic-funny remark, those discussions around dark mode for WinForms app shows the high participation of the community and the desire to make this work, and note also that other issues which have been pointed out in other projects show us clearly, why we should accomodate rendering issues as early as possible to unblock them: GitExtension in particular but also other projects can provide their aspired .NET 10 based DarkMode-enabled versions as soon as .NET 10 becomes available.

Fixes rendering issues in dark mode rendering, where a button is used in the context of another control:

• DropDownArrow
• UpDown based controls
• Ellipse-Control in Property browsers

These buttons have not been rendered correctly in dark mode, and a new system control button renderer (tested by CTI) fixes these issues.

Note that this PR does not change the Classic (Light Mode) code paths in any way.

Examples:

---

---

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Current versions have been tested by CTI and they also reassured that the Classic mode CodePaths (LightMode rendering) remain unchanged to minimize any risks.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

❌ Patch coverage is 33.10023% with 287 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.87326%. Comparing base (fbd28a7) to head (c35b79a).
⚠️ Report is 5 commits behind head on release/10.0-preview7.

Additional details and impacted files

@@                       Coverage Diff                       @@
##           release/10.0-preview7      #13748         +/-   ##
===============================================================
- Coverage               76.90985%   76.87326%   -0.03660%     
===============================================================
  Files                       3260        3261          +1     
  Lines                     643088      643411        +323     
  Branches                   47601       47625         +24     
===============================================================
+ Hits                      494598      494611         +13     
- Misses                    144830      145137        +307     
- Partials                    3660        3663          +3     

Flag	Coverage Δ
Debug	76.87326% <33.10023%> (-0.03660%)	⬇️
integration	18.97943% <30.53613%> (-0.01510%)	⬇️
production	51.52889% <33.10023%> (-0.05333%)	⬇️
test	97.42152% <ø> (ø)
unit	48.91751% <25.40793%> (-0.04309%)	⬇️

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[merriemcgaw]

Critical fix for Dark Mode users