Fix FontSource/FontFileStream embedded resource memory leak

[h3xds1nz]

Fixes #7289

Description

Fixes memory leak when using fonts from embedded resources that are materialized onto FontSource -> FontFamily, etc.

The issue is basically in FontSource.GetUnmanagedStream():

• We're passing around pure UnmanagedMemoryStream instance, but life without destructor is kind of hard.
  • This can be removed once FontFileStream from DirectWriteForwarder would be migrated to C#.

More context: The fix could be done by disposing the UnmanagedMemoryStream instantly and wrapping it in a new instance so it's cleared from the List<Stream> of PackagePart but I think it's nice to tie the lifetime together.

Customer Impact

Customers will finally get their fix after 10 years.

https://stackoverflow.com/questions/31452443/wpf-textblock-memory-leak-when-using-font
https://stackoverflow.com/questions/49550759/wpf-load-font-from-resources
https://stackoverflow.com/questions/45297837/what-causes-unmanagedmemorystream-in-wpf-memory-leak
https://stackoverflow.com/questions/39157846/wpf-glyphs-control-font-uriits-slow-and-remains-in-memory

Regression

Has been around since at least .NET 4.5.

Testing

Using the repro in #7289; sample apps use.

Risk

Low though we're passing around stuff onto C++/CLI, that's always awful.

Microsoft Reviewers: Open in CodeFlow

[Symbai]

Customers will finally get their fix after 10 years.

❤️❤️❤️

[miloush]

LGTM

[poutine70]

What is the status of this issue? Anyfix soon?

[himgoyalmicro]

LGTM

[himgoyalmicro]

@h3xds1nz this PR is good to be merged. Can you please resolve the merge conflicts and the conversations.

[h3xds1nz]

@himgoyalmicro Resolved :)

P.S. I'd consider backporting this to NetFX given that you've backported the XPS one as well. For some apps this is rather a big issue.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.

Project coverage is 11.41724%. Comparing base (73c7e63) to head (fbaf8b5).
Report is 4 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main       #9948         +/-   ##
===================================================
- Coverage   11.55182%   11.41724%   -0.13458%     
===================================================
  Files           3214        3214                 
  Lines         648495      648502          +7     
  Branches       71512       71510          -2     
===================================================
- Hits           74913       74041        -872     
- Misses        572419      573303        +884     
+ Partials        1163        1158          -5     

Flag	Coverage Δ
Debug	11.41724% <0.00000%> (-0.13458%)	⬇️

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[himgoyalmicro]

Thank you @h3xds1nz for your continuous contributions! 😄
Regarding the backporting, we will discuss it with the internal review team.

[h3xds1nz]

@himgoyalmicro Thank you, maybe I'll fix some more stuff then 😀