RFR: 8373366: HandshakeState should disallow suspend ops for disabler threads [v2]

[Serguei Spitsyn]

> This update fixes the following problem. The function JavaThread::java_suspend has the following assert:
> 
>  bool JavaThread::java_suspend(bool register_vthread_SR) {
>    // Suspending a vthread transition disabler can cause deadlocks.
>   assert(!is_vthread_transition_disabler(), "no suspend allowed for vthread transition disablers");
>   . . .
> 
> This is an over-hard requirement/invariant for threads that execute JVMTI functions (e.g. in an agent event handler). Such threads need a chance to be eventually suspended after JVMTI function completes its work and its `mountUnmountDisabler` is destructed.
> 
> A more adequate approach is to tweak the function
> `HandshakeOperation* HandshakeState::get_op_for_self(bool allow_suspend, bool check_async_exception)`
> so it could skip a `HandshakeOperation` if `_handshakee->is_vthread_transition_disabler() == true`, so the same temporary suspension disabling mechanism would be used as for `_handshakee->is_disable_suspend() == true`.
> 
> Testing:
>  - In progress: mach5 tiers 1-6

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

  review: restored the assert and fixed the issue caused it to fire

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28740/files
  - new: https://git.openjdk.org/jdk/pull/28740/files/8c25f690..b51267f3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28740&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28740&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28740.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28740/head:pull/28740

PR: https://git.openjdk.org/jdk/pull/28740