[jdk21u-dev] RFR: 8324969: C2: prevent elimination of unbalanced coarsened locking regions

[Martin Doerr]

Backport of [JDK-8324969](https://bugs.openjdk.org/browse/JDK-8324969). Applies cleanly except `+#include "opto/locknode.hpp"` in escape.cpp which is integrated manually because of unrelated context changes.

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Commit messages:
 - b938a5c9edd53821a52b43a8e342b76adb341a3f

Changes: https://git.openjdk.org/jdk21u-dev/pull/700/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=700&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324969
  Stats: 273 lines in 9 files changed: 255 ins; 2 del; 16 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/700.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/700/head:pull/700

PR: https://git.openjdk.org/jdk21u-dev/pull/700