RFR: 8333542: Breakpoint in parallel code does not work

[Coleen Phillimore]

Revert the change for JDK-8288064 "Class initialization locking".  JVMTI class prepare event relies on a lock being held through setting the state of the class to 'linked' and the JVMTI event posting. The only usable lock is the Java object init_lock, which was removed.  This change restores the lock and fixes all the conflicts in code that's changed since.

Tested with tier1-7.

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Commit messages:
 - NULL -> nullptr
 - NULL -> nullptr
 - Include synchronizer.hpp in instanceKlass.cpp
 - Add a test contributed by Chris Plummer.
 - Include synchronizer.hpp in cpCache.cpp
 - Fix JVMCI again.
 - Revert "8288064: Class initialization locking"

Changes: https://git.openjdk.org/jdk/pull/19755/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19755&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333542
  Stats: 516 lines in 16 files changed: 339 ins; 129 del; 48 mod
  Patch: https://git.openjdk.org/jdk/pull/19755.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19755/head:pull/19755

PR: https://git.openjdk.org/jdk/pull/19755