JIT: handle commas during inline return value substitution

[AndyAyersMS]

Fixes #119058.

[Copilot]

Pull Request Overview

This PR fixes a JIT assertion failure during inline return value substitution when handling comma operators. The issue occurred when a conditional jump (jtrue) had a comma operation as its condition, causing the JIT to fail during flow graph optimization.

Key changes:

• Adds handling for comma operations in conditional statements during inline substitution
• Extracts side effects from comma operations into separate statements
• Includes a regression test to prevent this issue from reoccurring

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/coreclr/jit/fginline.cpp	Adds logic to handle comma operations in jtrue statements by extracting side effects and splicing out the comma
src/tests/JIT/Regression/JitBlue/Runtime_119508/Runtime_119508.cs	Regression test that reproduces the original JIT assertion failure scenario
src/tests/JIT/Regression/JitBlue/Runtime_119508/Runtime_119508.csproj	Project file for the regression test with optimization enabled

[AndyAyersMS]

@dotnet/jit-contrib PTAL

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[AndyAyersMS]

Also we don't really need to extra all side effects, just tunnel down through until we find a compare or constant. Maybe I should rework this as a split.

[AndyAyersMS]

@EgorBo updated; can you take one more look?

[AndyAyersMS]

@EgorBo ping

[AndyAyersMS]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/17407078615