RFR: 8336299: Improve GCLocker stall diagnostics [v3]

[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.
> 
> Example log messages
> 
> 1. Last thread exiting. Performing GC after exiting critical section. Thread "main" 0 locked.
> 
> 2. Thread exiting critical region Thread "main" 0 locked.
> 
> 3. Thread stalled by JNI critical section. Resumed after 586ms. Thread "Thread-0".
> 
> 4. Thread blocked to enter critical region. Resumed after 1240ms. Thread "SIGINT handler".

Neethu Prasad has updated the pull request incrementally with one additional commit since the last revision:

  Add missing imports and remove unused ones

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20277/files
  - new: https://git.openjdk.org/jdk/pull/20277/files/b2185185..c6b66ceb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20277&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20277&range=01-02

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 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