RFR: 8296324: JVMTI GetStackTrace truncates vthread stack trace for agents loaded into running VM [v3]

[Serguei Spitsyn]

> The `VirtualThread` static field `notifyJvmtiEvents` is not set correctly in cases JVMTI agents are loaded into running VM. It is because an extra call to java_lang_VirtualThread::init_static_notify_jvmti_events() is needed.
> This function is called once at the VM initialization, so this extra call is not necessary for agent loaded at startup.
> 
> Testing:
> New test is added: `test/hotspot/jtreg/serviceability/jvmti/vthread/VirtualStackTraceTest`
> This test is failed without fix and passed with it.
> TBD: run all JVMTI and JDI test in mach5.

Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:

  ajust condition when init_static_notify_jvmti_events() is called

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11204/files
  - new: https://git.openjdk.org/jdk/pull/11204/files/5a15a6da..a3123386

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11204&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11204&range=01-02

  Stats: 6 lines in 1 file changed: 0 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/11204.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11204/head:pull/11204

PR: https://git.openjdk.org/jdk/pull/11204