RFR: 8316397: StackTrace/Suspended/GetStackTraceSuspendedStressTest.java failed with: SingleStep event is NOT expected

[Serguei Spitsyn]

The JVMTI functions `SuspendThread()`, `SuspendThreadList()` and `SuspendAllVirtualThreads()` use the runtime `HandshakeState::suspend()` function `SuspendThreadHandshake` class to suspend the `JavaThread` of a mounted virtual thread. They work under protection of the `JvmtiVTMSTransitionDisabler` to make the association of virtual thread with `JavaThread` stable. The function `HandshakeState::suspend()` creates an instance of`SuspendThreadHandshake`, executes it synchronously and then just returns. The `SuspendThreadHandshake:: do_thread()` in its order create an instance of the `ThreadSelfSuspensionHandshake` (which is a subclass of the `AsyncHandshakeClosure`) to force the handshakee's self-suspension asynchronously. The `HandshakeState::suspend()` does not wait for target thread real self-suspension, nor reaching a safe thread state that can be treated as a suspend-equivalent. This creates problems as the target virtual thread's activity can be observable after the JVMTI `Suspend
 Thread()` and others are returned. For instance, some `SingleStep` events can be posted.
The fix is to wait in the `HandshakeState::suspend()` for the target handshakee to reach a safe thread state. This is done for the virtual thread case only. The suspension of normal platform threads remains the same.

Testing:
 - Ran mach5 tiers 1-6

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Commit messages:
 - 8316397: StackTrace/Suspended/GetStackTraceSuspendedStressTest.java failed with: SingleStep event is NOT expected

Changes: https://git.openjdk.org/jdk/pull/23490/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23490&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316397
  Stats: 22 lines in 2 files changed: 22 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23490.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23490/head:pull/23490

PR: https://git.openjdk.org/jdk/pull/23490