RFR: 8331691: Generational ZGC: Use ZLocker uniformly

[Guoxiong Li]

Hi all,

This patch removes the classes `ZDriverLocker` and `ZDriverUnlocker`, and uses `ZLocker` and newly added `ZUnlocker` instead. Thanks for taking the time to review.

Testing:
- [ ] linux-x64-slowdebug test-hotspot_gc

Best Regards,
-- Guoxiong

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Commit messages:
 - Use ZLocker unified.

Changes: https://git.openjdk.org/jdk/pull/19092/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19092&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331691
  Stats: 79 lines in 5 files changed: 25 ins; 38 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/19092.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19092/head:pull/19092

PR: https://git.openjdk.org/jdk/pull/19092