RFR: 8306034: add support of virtual threads to JVMTI StopThread

[Serguei Spitsyn]

This enhancement adds support of virtual threads to the JVMTI `StopThread` function.
In preview releases before this enhancement the StopThread returned the JVMTI_ERROR_UNSUPPORTED_OPERATION error code for virtual threads.

The `StopThread` supports sending an asynchronous exception to a virtual thread only if it is current or suspended at mounted state. For instance, a virtual thread can be suspended at a JVMTI event. If the virtual thread is not suspended and is not current then the `JVMTI_ERROR_THREAD_NOT_SUSPENDED` error code is returned. If the virtual thread was suspended at unmounted state then the `JVMTI_ERROR_OPAQUE_FRAME` error code is returned.

The `StopThread` has the following description for `JVMTI_ERROR_OPAQUE_FRAME` error code:
> The thread is a suspended virtual thread and the implementation 
> was unable to throw an asynchronous exception from this frame.

A couple of the `serviceability/jvmti/vthread` tests has been updated to adopt to new `StopThread` behavior.

The CSR is: https://bugs.openjdk.org/browse/JDK-8306434

Testing:
The mach5 tears 1-6 are in progress.
Preliminary test runs were good in general.
The JDB test `vmTestbase/nsk/jdb/kill/kill001/kill001.java` has been problem-listed and will be fixed by the corresponding debugger enhancement which is going to adopt JDWP/JDI specs to new behavior of the JVMTI `StopThread` related to virtual threads.

Also, two JCK JVMTI tests are failing in the tier-6 :
> vm/jvmti/StopThread/stop001/stop00103/stop00103.html
> vm/jvmti/StopThread/stop001/stop00103/stop00103a.html

These two tests will be excluded from the test runs by the JCK team and then adjusted to new `StopThread` behavior.

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Commit messages:
 - fixed trailing spaces
 - 8306034: add support of virtual threads to JVMTI StopThread

Changes: https://git.openjdk.org/jdk/pull/13546/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13546&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306034
  Stats: 477 lines in 8 files changed: 456 ins; 8 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/13546.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13546/head:pull/13546

PR: https://git.openjdk.org/jdk/pull/13546