Revert backflow and re-apply VMR build

[mmitche]

No description provided.

[Copilot]

Pull Request Overview

This PR reverts backflow changes and re-applies VMR build updates. The changes primarily focus on improving test coverage in nativeaot smoke tests and making refinements to garbage collection (GC) logic, particularly for background GC handling of UOH (Uniform Object Heap) allocations.

Key Changes

• Enhanced test coverage for nativeaot reflection scenarios including activation without constructors and nested generic types
• Refined garbage collection logic for UOH allocations during background GC with improved allocation action determination
• Updated XHarness configuration by removing LaunchTimeout parameters and adding null argument validation tests

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/tests/nativeaot/SmokeTests/Reflection/Reflection.cs	Adds new test classes for activation without constructors and nested generic type creation
src/tests/nativeaot/SmokeTests/DynamicGenerics/Github118072.cs	Simplifies cache flushing logic using GC collection instead of type creation
src/tests/Common/helixpublishwitharcade.proj	Removes LaunchTimeout configuration from XHarness test bundles
src/libraries/sendtohelix-mobile.targets	Removes LaunchTimeout parameters from mobile test configurations
src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/FilePatternMatchTests.cs	Adds null argument exception tests for FilePatternMatch constructor
src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Internal/PatternTestResult.cs	Adds MemberNotNullWhen attribute for better null analysis
src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/FilePatternMatch.cs	Changes Stem property from nullable to non-nullable string with validation
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/HandleCallAction.cs	Improves MakeGenericType handling for reference type instantiations
src/coreclr/gc/gcpriv.h	Refactors UOH allocation tracking from separate LOH/POH variables to unified arrays
src/coreclr/gc/gcconfig.h	Adds UOHWaitBGCSizeIncPercent configuration option
src/coreclr/gc/gc.cpp	Implements new UOH allocation action logic during background GC with configurable thresholds

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[jeffhandley]

This matches the expected revert of the "Backflow from https://github.com/dotnet/dotnet / ca3dd2c build 278938" commit, bef141f.

I also confirmed that the other recent Backflow commit (7c3ad07) in the PR did not have the effect of reverting other PRs.

[MichalStrehovsky]

/ba-g networking timeouts on android that look unrelated