RFR: 8295976: GetThreadListStackTraces returns wrong state for blocked VirtualThread [v2]

[Serguei Spitsyn]

> The `GetThreadListStackTraces` returns `JVMTI_THREAD_STATE_RUNNABLE` for a VirtualThread blocked on a monitor when called for more than one thread. When called for a single VirtualThread it correctly returns a state that includes the `JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER` flag.
> The `VM_GetThreadListStackTraces::doit` should call the `get_threadOop_and_JavaThread` instead of `cv_external_thread_to_JavaThread`. But the `get_threadOop_and_JavaThread` has a check for the current thread by comparing with the JavaThread::current() which does not work for a `VM_op`. Some refactoring of the `GetSingleStackTraceClosure` and `get_threadOop_and_JavaThread` was made to make it working for a `VM_op`.
> 
> Also, a minor bug in the `GetSingleStackTraceClosure::do_thread()` was discovered during testing.
> A minor refactoring of the `GetSingleStackTraceClosure` was made to fix the issue.
> 
> Also, a new test was added to provide coverage:
>  - `test/hotspot/jtreg/serviceability/jvmti/vthread/ThreadListStackTracesTest`
>  
> Testing:
>  - ran new test: `test/hotspot/jtreg/serviceability/jvmti/vthread/ThreadListStackTracesTest`
>  - TBD: tiers 1-6

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

  simplify GetSingleStackTraceClosure, fix issue in VM_GetThreadListStackTraces::doit, improve test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14326/files
  - new: https://git.openjdk.org/jdk/pull/14326/files/77718470..4e794bd5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14326&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14326&range=00-01

  Stats: 27 lines in 4 files changed: 11 ins; 5 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/14326.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14326/head:pull/14326

PR: https://git.openjdk.org/jdk/pull/14326