RFR: 8286285: Rank issues with ParGCRareEvent_lock and Threads_lock

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that fixes up the rank of the `ParGCRareEvent_lock` lock? It might be called in the vm-thread that holds the `Threads_lock` during (single-threaded) verification.

Testing: gha, local testing inducing uses of `ParGCRareEvent_lock` in the VM thread

Thanks,
  Thomas

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Commit messages:
 - initial changes

Changes: https://git.openjdk.java.net/jdk/pull/8573/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8573&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286285
  Stats: 7 lines in 2 files changed: 2 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8573.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8573/head:pull/8573

PR: https://git.openjdk.java.net/jdk/pull/8573