[lworld] RFR: 8335545: [lworld] JNI MonitorEnter doesn't throw the right exception

[Frederic Parain]

Fix JNI's MonitorEnter to throw IdentityException instead of IllegalMonitorStateException.

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Commit messages:
 - Fix exception thrown by MonitorEnter

Changes: https://git.openjdk.org/valhalla/pull/1160/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1160&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335545
  Stats: 48 lines in 2 files changed: 25 ins; 12 del; 11 mod
  Patch: https://git.openjdk.org/valhalla/pull/1160.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1160/head:pull/1160

PR: https://git.openjdk.org/valhalla/pull/1160