Replace ArrayList from FrameworkElement with List<TemplateKey>

[h3xds1nz]

Description

Replaces ArrayList with List<TemplateKey> to increase type safety and promote strongly-typed code. Most of the perf benefits beyond t0 were now erased in post .NET 9 as the ArrayList methods are usually successfully de-abstracted but that doesn't really matter as its still a benefit to use a generic collection type instead e.g. to bypass cast checks.

Customer Impact

Cleaner codebase for developers.

Regression

No.

Testing

Local build.

Risk

Low, just a type swap on private collection.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.

Project coverage is 10.94648%. Comparing base (2ded801) to head (67b3c5f).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10700         +/-   ##
===================================================
- Coverage   10.95887%   10.94648%   -0.01239%     
===================================================
  Files           3310        3310                 
  Lines         664667      664661          -6     
  Branches       74667       74666          -1     
===================================================
- Hits           72840       72757         -83     
- Misses        590685      590770         +85     
+ Partials        1142        1134          -8     

Flag	Coverage Δ
Debug	10.94648% <0.00000%> (-0.01239%)	⬇️

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