[lworld] RFR: 8310023: [lworld] Implement alternative fast-locking scheme in Valhalla

[Coleen Phillimore]

I don't see anything missing for implementing the test for inline types for lightweight locking.  The only thing broken seems to be JNI monitorenter should throw IdentityException.  I added some comments and asserts when I figured out the interpreter and c1/c2 don't get to ObjectSynchronizer::enter.
Tested with tier1 with LM_LIGHTWEIGHT as the default.

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Commit messages:
 - Add some comments and asserts.
 - Shouldn't JNI enter throw IdentityException too?
 - 8310023: [lworld] Implement alternative fast-locking scheme in Valhalla

Changes: https://git.openjdk.org/valhalla/pull/1158/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1158&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310023
  Stats: 29 lines in 3 files changed: 15 ins; 4 del; 10 mod
  Patch: https://git.openjdk.org/valhalla/pull/1158.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1158/head:pull/1158

PR: https://git.openjdk.org/valhalla/pull/1158