JIT: Make async tail merging layout equality assert a check

[jakobbotsch]

#128704 shows that the comment is false. Just make the assert a real check until I have time to look into why it wouldn't be true.

Fix #128704

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[Copilot]

Pull request overview

This PR backs out the async suspension tail-merge optimization in the CoreCLR JIT to avoid the ContinuationLayoutBuilder::Equals assertion failure reported in #128704.

Changes:

• Removes the async suspension reuse/merge path and its associated metric.
• Removes helper comparison APIs that were only used by the merge logic.
• Restores per-suspension state creation while keeping existing continuation layout/reuse flow intact.

Reviewed changes

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/jit/jitmetadatalist.h	Removes the now-unused SuspensionPointsMerged JIT metric.
src/coreclr/jit/gentree.h	Removes the unused GenTreeLclVarCommon::EqualsLocal declaration.
src/coreclr/jit/gentree.cpp	Removes the EqualsLocal implementation formerly used by async suspension merging.
src/coreclr/jit/async.h	Removes declarations for suspension reuse helpers and updates suspension fill signature.
src/coreclr/jit/async.cpp	Removes suspension tail-merge logic and always creates a distinct suspension state per async call.

[jakobbotsch]

cc @dotnet/jit-contrib PTAL @AndyAyersMS

[jakobbotsch]

/ba-g Simple change, merging to fix innerloop