[master] RFR: OMWorld: Cleanup quick_enter

[Axel Boldt-Christmas]

Cleanup of `ObjectSynchronizer::quick_enter` after `LM_LIGHTWEIGHT` and `LM_PLACEHOLDER` got merged.

`LM_LIGHTWEIGHT` now makes use of `quick_enter`.  Doing a lookup in the hash table may be not be the best thing to do. Maybe just looking in thread local cache is enough. To avoid having to do multiple lookups.  Will add this change after I have tested it.

This commit is currently based on ffc4c2fd5ba1c28432a5d5e84b8ada95fba7eeb8 without a merge. So GHA is not tested with lilliput. As long as this is mergable without conflicts (and no manual merge is performed) it will also be possible to move this commit down below lilliput on-top of OMWorld directly.

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Commit messages:
 - OMWorld: Cleanup quick_enter

Changes: https://git.openjdk.org/lilliput/pull/157/files
  Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=157&range=00
  Stats: 6 lines in 1 file changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/lilliput/pull/157.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/157/head:pull/157

PR: https://git.openjdk.org/lilliput/pull/157