RFR: 8330146: assert(!_thread->is_in_any_VTMS_transition()) failed

[Serguei Spitsyn]

Any event posting code except CFLH, ClassPrepare and ClassLoad  events has a conditional return in case if the event is posted during a VTMS transition. The CFLH, ClassPrepare and ClassLoad event posting code has just an assert instead. The ClassPrepare and ClassLoad events also have a conditional return in a case of temporary VTMS transition.
This update is to align the CFLH, ClassPrepare and ClassLoad events with all other events in this area.

Testing:
 - TBD: submit mach5 tiers 1-6

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Commit messages:
 - 8330146: assert(!_thread->is_in_any_VTMS_transition()) failed

Changes: https://git.openjdk.org/jdk/pull/19054/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19054&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330146
  Stats: 9 lines in 1 file changed: 2 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/19054.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19054/head:pull/19054

PR: https://git.openjdk.org/jdk/pull/19054