Small default font scaling corrections and optimizations. Fix #11037.

[kirsan31]

Fixes #11037

Proposed changes

• Сhange the default font only if it has really changed. Most of these problems already was solved in f36b0db.
• Not use scaled default font for system fonts.
• Not dispose user (external) fonts.

Customer Impact

• Fewer font changing related actions and a bit less memory use.
• Bug fixes.

Regression?

• Yes

Risk

• Minimal.

Test methodology

• Existing unit tests.
• New unit tests.
• Manually with test app: DefFontTest.zip

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 60.43956% with 36 lines in your changes are missing coverage. Please review.

Project coverage is 73.47415%. Comparing base (d9e9d93) to head (df91fcc).
Report is 46 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #11206         +/-   ##
===================================================
+ Coverage   73.44664%   73.47415%   +0.02750%     
===================================================
  Files           3098        3101          +3     
  Lines         632225      632515        +290     
  Branches       46653       46706         +53     
===================================================
+ Hits          464348      464735        +387     
+ Misses        164485      164369        -116     
- Partials        3392        3411         +19     

Flag	Coverage Δ
Debug	73.47415% <60.43956%> (+0.02750%)	⬆️
integration	18.35905% <0.00000%> (-0.00289%)	⬇️
production	46.96613% <44.18605%> (+0.05460%)	⬆️
test	94.98574% <75.00000%> (-0.00025%)	⬇️
unit	43.93455% <44.18605%> (+0.05695%)	⬆️

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