RFR: 8306028: separate ThreadStart/ThreadEnd events posting code in JVMTI VTMS transitions [v3]

[Serguei Spitsyn]

> This refactoring to separate ThreadStart/ThreadEnd events posting code in the JVMTI VTMS transitions is needed for future work on JVMTI scalability and performance improvements. It is to easier put this code on slow path.
> 
> Testing: mach5 tiers 1-6 were successful.

Serguei Spitsyn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge
 - 8304444: Reappearance of NULL in jvmtiThreadState.cpp
 - 8306028: separate ThreadStart/ThreadEnd events posting code in JVMTI VTMS transitions

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13484/files
  - new: https://git.openjdk.org/jdk/pull/13484/files/7735ffac..5594635c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13484&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13484&range=01-02

  Stats: 224828 lines in 1318 files changed: 212269 ins; 4015 del; 8544 mod
  Patch: https://git.openjdk.org/jdk/pull/13484.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13484/head:pull/13484

PR: https://git.openjdk.org/jdk/pull/13484