[MTP] Improve performance of validating command line options

[Copilot]

This PR improves the performance of CommandLineOptionsValidator which was consuming an unnecessarily large amount of CPU time as identified in a trace involving multiple test processes.

Performance improvements:

Algorithm Optimizations

• Reduced algorithmic complexity from O(n²) to O(n) in critical validation methods
• Replaced expensive LINQ operation chains with direct data structure access
• Optimized ValidateNoUnknownOptions by using a HashSet for O(1) lookups instead of nested LINQ operations

Memory Allocations

• Optimized ToTrimmedString to avoid unnecessary string allocations
• Created StringBuilder instances only when needed instead of always pre-allocating
• Reduced intermediate collection creation during validation

Data Structure Improvements

• Used HashSet and Dictionary for fast lookups instead of repeated LINQ operations
• Eliminated expensive Union() and Intersect() operations with direct dictionary operations

Documentation

• Added PerformanceSensitive attribute to document performance-critical code paths
• Annotated all validation methods with appropriate performance attributes

Before Optimization

Fixes #5651.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• kmuvsblobprodcus389.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/testfx/testfx/.dotnet/dotnet msbuild /m /nologo /clp:Summary /v:minimal /nr:true /warnaserror /p:TreatWarningsAsErrors=true /p:ContinuousIntegrationBuild=false /home/REDACTED/work/testfx/testfx/artifacts/toolset/restore.proj /t:__WriteToolsetLocation /clp:ErrorsOnly;NoSummary /p:__ToolsetLocationOutputFile=/home/REDACTED/work/testfx/testfx/artifacts/toolset/10.0.0-beta.25229.4.txt (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.32%. Comparing base (65f8636) to head (97c8299).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5655      +/-   ##
==========================================
- Coverage   76.37%   76.32%   -0.05%     
==========================================
  Files         602      602              
  Lines       36759    36813      +54     
==========================================
+ Hits        28075    28099      +24     
- Misses       8684     8714      +30     

Flag	Coverage Δ
Debug	76.32% <100.00%> (-0.05%)	⬇️
integration	76.32% <100.00%> (-0.05%)	⬇️
production	76.32% <100.00%> (-0.05%)	⬇️
unit	76.33% <100.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...latform/CommandLine/CommandLineOptionsValidator.cs	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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