RFR: 8334594: Generational ZGC: Deadlock after OopMap rewrites in 8331572

[Aleksey Shipilev]

As shown in the bug, there are cases when acquiring the `ServiceLock` for opportunistic notification leads to deadlock. We can untie the deadlock by checking if `ServiceLock` can be acquired on triggering path, and never blocking otherwise.

Additional testing:
 - [ ] Linux x86_64 service fastdebug, `all`
 - [ ] Linux AArch64 service fastdebug, `all`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/19800/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19800&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334594
  Stats: 12 lines in 6 files changed: 3 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/19800.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19800/head:pull/19800

PR: https://git.openjdk.org/jdk/pull/19800