[jdk21u] RFR: 8315869: UseHeavyMonitors not used

[Aleksey Shipilev]

Unclean backport to clean up JDK 21 and make future backports more clean. The removed option is `develop`, so there is no compatibility problems.

The uncleanliness comes from the need to `-XX:+UnlockExperimentalVMOptions` the flag.

Additional testing:
 - [x] `grep -R UseHeavyMonitors src/`, no hits
 - [x] `grep -R UseHeavyMonitors test/`, no hits
 - [x] macos-aarch64-server-fastdebug, affected tests pass
 - [x] macos-aarch64-server-release, affected tests pass

-------------

Commit messages:
 - Unlock LockingMode properly
 - Backport 3301fb1e8ad11d7de01a052e0a2d6178a7579ba6

Changes: https://git.openjdk.org/jdk21u/pull/265/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=265&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315869
  Stats: 16 lines in 4 files changed: 0 ins; 13 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u/pull/265.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/265/head:pull/265

PR: https://git.openjdk.org/jdk21u/pull/265