RFR: 8297286: runtime/vthread tests crashing after JDK-8296324 [v9]

[Serguei Spitsyn]

> The fix is to enable virtual threads support for late binding JVMTI agents.
> The fix includes:
> - New function `JvmtiEnvBase::enable_virtual_threads_notify_jvmti()` which does enabling JVMTI VTMS transition notifications in case of agent loaded into running VM. This function executes a VM operation counting VTMS transition bits in all `JavaThread`'s to correctly set the static counter `_VTMS_transition_count` needed for VTMS transition protocol.
> - New function `JvmtiEnvBase::disable_virtual_threads_notify_jvmti()` which is needed for testing. It is used by the `WhiteBox` API.
> - New WhiteBox function `WB_SetVirtualThreadsNotifyJvmtiMode(JNIEnv* env, jobject wb, jboolean enable)` needed for testing of this update.
> - New regression test: `serviceability/jvmti/vthread/ToggleNotifyJvmtiTest`
> 
> Testing:
> - New test: `serviceability/jvmti/vthread/ToggleNotifyJvmtiTest`
> - The originally failed tests are expected to pass now:
>   `runtime/vthread/RedefineClass.java`
>   `runtime/vthread/TestObjectAllocationSampleEvent.java` 
> - In progress: Run the tiers 1-6 to make sure there are no regression.

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

  review: updated correction of jt->jvmti_thread_state() links in VM_SetNotifyJvmtiEventsMode

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13133/files
  - new: https://git.openjdk.org/jdk/pull/13133/files/2c59c54b..c5d8a015

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13133&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13133&range=07-08

  Stats: 14 lines in 1 file changed: 4 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/13133.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13133/head:pull/13133

PR: https://git.openjdk.org/jdk/pull/13133