Changes and testing for 12042 review

[pcblues]

Fixes #12042 - TreeNode and ListItem not displaying in dark mode during editing, even though application is set to be in dark mode.

Proposed changes

If the application is in dark mode, capture the parent's windows message to identify the start of editing, and change the colour of the brush to match the parent's window color.

Customer Impact

Correction of incorrect color selection.

Regression?

• Yes / No

Risk

I tried to limit the impact of the change to only occurring when the application is in dark mode. I'm not sure of the impact, if any, on custom ListView subitems, or custom-drawn TreeNodes.

Screenshots

Before

After

Test methodology

I used the test application provided to highlight the bug in the ticket to test the new behaviour.

Note that I added the following lines (uncommitted) to tests\integration\WinformsControlsTest\Program.cs
in order to enable dark mode.

It made the buttons look hard to read.
//Application.EnableVisualStyles();
//Application.SetHighDpiMode(HighDpiMode.PerMonitorV2);
#pragma warning disable WFO5001
Application.SetColorMode(SystemColorMode.Dark);

I haven't tested with the commented out option uncommented.

Accessibility testing

Test environment(s)

Microsoft Reviewers: Open in CodeFlow

Microsoft Reviewers: Open in CodeFlow

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.77351%. Comparing base (851d52d) to head (8a01a47).

Additional details and impacted files

@@                 Coverage Diff                  @@
##                main      #13245          +/-   ##
====================================================
+ Coverage   39.78342%   61.77351%   +21.99009%     
====================================================
  Files           1018        1552         +534     
  Lines          96407      158950       +62543     
  Branches       13451       14803        +1352     
====================================================
+ Hits           38354       98189       +59835     
- Misses         57654       60046        +2392     
- Partials         399         715         +316     

Flag	Coverage Δ
Debug	61.77351% <ø> (+21.99009%)	⬆️
integration	10.72623% <ø> (-0.00106%)	⬇️
production	39.78342% <ø> (ø)
test	95.67018% <ø> (?)
unit	37.22448% <ø> (+0.00104%)	⬆️

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