RFR: 8304738: UnregisteredClassesTable_lock never created

Wed Apr 5 17:09:14 UTC 2023

UnregisteredClassesTable_lock is never created in mutex_init() and is always nullptr. This lock is referenced in a few places and all of those are effectively thread unsafe. Some of the places `unregistered_classes_table` is accessed are under other locks, so the rank of this lock has to be adjusted appropriately. The lock will be initialized to enable the intended behavior. Verified with tier 1-4 tests.

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Commit messages:
 - 8304738: UnregisteredClassesTable_lock never created

Changes: https://git.openjdk.org/jdk/pull/13358/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13358&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304738
  Stats: 3 lines in 2 files changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13358.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13358/head:pull/13358

PR: https://git.openjdk.org/jdk/pull/13358