RFR: 8340796: Use a consistent order when loading cxq and EntryList [v2]

[Fredrik Bredberg]

> Made sure we use a consistent order when reading ObjectMonitor EntryList and cxq while exiting the monitor.
> That consistent order is EntryList before cxq. Added a comment in the shared code to explaining why it's okay that waiters slip undetected between reading EntryList and cxq.
> 
> Tested ok tier1-3.

Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:

  Update after review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21584/files
  - new: https://git.openjdk.org/jdk/pull/21584/files/21da21e5..f1ef577a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21584&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21584&range=00-01

  Stats: 33 lines in 6 files changed: 0 ins; 16 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/21584.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21584/head:pull/21584

PR: https://git.openjdk.org/jdk/pull/21584