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

[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.

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Commit messages:
 - fixed traling whitespace in jvmtiExport.cpp
 - 8296324: JVMTI GetStackTrace truncates vthread stack trace for agents loaded into running VM

Changes: https://git.openjdk.org/jdk/pull/11204/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11204&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296324
  Stats: 182 lines in 3 files changed: 181 ins; 0 del; 1 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