RFR: 8369482: JVMTI + Loom: JDK-8368159 introduced safepoint poll in disallowed state

[Axel Boldt-Christmas]

[JDK-8368159](https://bugs.openjdk.org/browse/JDK-8368159) added `JvmtiExport::has_frame_pops(JavaThread* thread)`
which calls `JvmtiExport::get_jvmti_thread_state();` which may safepoint.

Example stack trace:

V [libjvm.dylib+0x125f888] VMError::report(outputStream*, bool)+0x1b68 (javaThread.cpp:375)
V [libjvm.dylib+0x1263184] VMError::report_and_die(int, char const*, char const*, char*, Thread*, unsigned char*, void const*, void const*, char const*, int, unsigned long)+0x55c
V [libjvm.dylib+0x5de268] print_error_for_unit_test(char const*, char const*, char*)+0x0
V [libjvm.dylib+0x9427ec] JavaThread::check_for_valid_safepoint_state()+0x120
V [libjvm.dylib+0xe7e4e4] Mutex::lock(Thread*)+0x48
V [libjvm.dylib+0xbbb198] JvmtiThreadState::state_for(JavaThread*, Handle)+0x200
V [libjvm.dylib+0xc462ec] JvmtiEventControllerPrivate::thread_started(JavaThread*)+0x1a0
V [libjvm.dylib+0xc493a4] JvmtiExport::get_jvmti_thread_state(JavaThread*, bool)+0xc0
V [libjvm.dylib+0xc5078c] JvmtiExport::has_frame_pops(JavaThread*)+0x24
V [libjvm.dylib+0x59c398] freeze_epilog(JavaThread*, ContinuationWrapper&, freeze_result)+0xf8
V [libjvm.dylib+0x59b6e8] Config<(oop_kind)0, CardTableBarrierSet>::freeze(JavaThread*, long*)+0x6f4
V [libjvm.dylib+0x59a4d4] int freeze<Config<(oop_kind)0, CardTableBarrierSet>>(JavaThread*, long*)+0x108


I suggest we do double checked on `JvmtiExport::can_post_frame_pop()` and move the `ContinuationWrapper::SafepointOp` scope.

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Commit messages:
 - 8369482: JVMTI + Loom: JDK-8368159 introduced safepoint poll in disallowed state

Changes: https://git.openjdk.org/jdk/pull/27716/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27716&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369482
  Stats: 9 lines in 1 file changed: 5 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27716.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27716/head:pull/27716

PR: https://git.openjdk.org/jdk/pull/27716