Fix GetGenerationBounds under USE_REGIONS

[cshung]

Fixes#55965.

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Issue Details

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Do not merge, this is currently a work-in-progress.

Author:	cshung
Assignees:	-
Labels:	area-GC-coreclr
Milestone:	-

[Maoni0]

I haven't really looked at the changes in proftoeeinterfaceimpl.cpp, I'll defer to @davmason.

[davmason]

Just the minor things I made comments on, otherwise looks good to me. Thanks Andrew!

[cshung]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1174937983

[github-actions]

@cshung backporting to release/6.0 failed, the patch most likely resulted in conflicts:

$ git am --3way --ignore-whitespace --keep-non-patch changes.patch
Applying: DiagAddNewRegion prototype
Applying: Updating the table directly under a lock
error: sha1 information is lacking or useless (src/coreclr/gc/gc.cpp).
error: could not build fake ancestor
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0002 Updating the table directly under a lock
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!