Mark System.Private.Windows.Core as WPF as well

[JeremyKuhne]

WPF now depends on it as well, need to mark it so it is included in WPF references.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.73971%. Comparing base (7896a6e) to head (8291783).
Report is 5 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #12521         +/-   ##
===================================================
+ Coverage   75.73723%   75.73971%   +0.00248%     
===================================================
  Files           3157        3157                 
  Lines         636098      636097          -1     
  Branches       47003       47002          -1     
===================================================
+ Hits          481763      481778         +15     
+ Misses        150864      150855          -9     
+ Partials        3471        3464          -7     

Flag	Coverage Δ
Debug	75.73971% <ø> (+0.00248%)	⬆️
integration	18.18423% <ø> (+0.00641%)	⬆️
production	49.30498% <ø> (+0.00545%)	⬆️
test	97.04530% <ø> (ø)
unit	46.51857% <ø> (+0.00367%)	⬆️

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