RFR: 8336299: Improve GCLocker stall diagnostics

[Neethu Prasad]

**Notes**
Adding logs to get more visibility into how fast a thread resumes from allocation stall. 

**Testing**
* tier 1, tier 2, hotspot_gc tests.



Last thread exiting. Performing GC after exiting critical section. Thread "main" 0 locked.

Thread exiting critical region Thread "main" 0 locked.

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Commit messages:
 - 8336299: Improve GCLocker stall diagnostics

Changes: https://git.openjdk.org/jdk/pull/20277/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20277&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336299
  Stats: 26 lines in 2 files changed: 25 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20277.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20277/head:pull/20277

PR: https://git.openjdk.org/jdk/pull/20277