VSTestBridge: Handle TestPropertyAttributes.Trait instead of special casing specific properties

[Youssef1313]

Fixes #5642

Instead of special casing MSTestDiscoverer.TestCategory and TestObject.Traits, we instead use TestPropertyAttributes.Trait to determine whether a property is a trait.

When the property value is string[], we assume it's the "categories". Otherwise, we expect it to be KVP<string, string>[] which is a list of traits as key value pairs.

NOTE: NUnit needs this. See nunit/nunit3-vs-adapter#1258

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.29%. Comparing base (310d17a) to head (4c13c92).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5644      +/-   ##
==========================================
- Coverage   76.34%   76.29%   -0.06%     
==========================================
  Files         602      602              
  Lines       36758    36754       -4     
==========================================
- Hits        28063    28041      -22     
- Misses       8695     8713      +18     

Flag	Coverage Δ
Debug	76.29% <100.00%> (-0.06%)	⬇️
integration	76.29% <100.00%> (-0.05%)	⬇️
production	76.29% <100.00%> (-0.06%)	⬇️
unit	76.29% <100.00%> (-0.06%)	⬇️

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Files with missing lines	Coverage Δ
....VSTestBridge/ObjectModel/ObjectModelConverters.cs	92.11% <100.00%> (-0.19%)	⬇️

... and 10 files with indirect coverage changes

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[Youssef1313]

/backport to rel/3.9

[github-actions]

Started backporting to rel/3.9: https://github.com/microsoft/testfx/actions/runs/15270580401