Address additional TitleBar corner case issues

[KlausLoeffelmann]

We introduced a few new APIs around TitleBar control (independent of dark mode).

• They have been put behind the DarkMode experimental flag, although they weren't really dark-mode related, but "just" controlling some TitleBar properties equally in Light- and in DarkMode.
• When a Form needs to recreate a handle, they "lost" their settings, since we only applied the TitleBar settings initially.

Fixes #12991.
Fixes #12992.

Microsoft Reviewers: Open in CodeFlow

[JeremyKuhne]

It isn't clear from reading the comments what the exact ordering dependency is.

[codecov]

Codecov Report

Attention: Patch coverage is 36.00000% with 16 lines in your changes missing coverage. Please review.

Project coverage is 76.59400%. Comparing base (4b461fd) to head (2bb00bc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13560         +/-   ##
===================================================
- Coverage   76.60068%   76.59400%   -0.00669%     
===================================================
  Files           3230        3230                 
  Lines         639151      639161         +10     
  Branches       47295       47297          +2     
===================================================
- Hits          489594      489559         -35     
- Misses        145989      146019         +30     
- Partials        3568        3583         +15     

Flag	Coverage Δ
Debug	76.59400% <36.00000%> (-0.00669%)	⬇️
integration	18.79437% <36.00000%> (-0.00381%)	⬇️
production	50.99510% <36.00000%> (-0.01399%)	⬇️
test	97.40411% <ø> (ø)
unit	48.39395% <36.00000%> (+0.01156%)	⬆️

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