JIT: Skip rarely-run block expansion during flow opts when we have profile data

[amanasifkhalid]

Follow-up to #113896. Since we now run profile repair before most of the profile-sensitive post-morph opts, fgExpandRarelyRunBlocks isn't very useful for PGO scenarios.

[Copilot]

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Comments suppressed due to low confidence (1)

src/coreclr/jit/optimizer.cpp:2383

• Ensure unit tests cover both paths of this condition (when profile weights are in use and when they are not) to validate that the rarely-run block expansion behaves as expected.

if (!fgIsUsingProfileWeights())

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[amanasifkhalid]

Small diffs from fgOptimizeBranch considering more blocks during post-morph flow opts, now that fewer blocks are marked rarely-run.