RFR: 8378194: Protect process_pending_interp_only() work with JvmtiThreadState_lock

[Serguei Spitsyn]

The function `JvmtiThreadState::process_pending_interp_only()` should protect the check with `state->is_pending_interp_only_mode()` and call to `JvmtiEventController::enter_interp_only_mode(state)` with the `JvmtiThreadState_lock`. Some level of optimization with a check of `seen_interp_only_mode()` is used as the code path of the `process_pending_interp_only()` is hot. Then the `seen_interp_only_mode()` has to be set somewhat earlier when the `is_pending_interp_only_mode()` is set.
This issue was discovered when in the work on the PR update of https://bugs.openjdk.org/browse/JDK-8373367 .

Testing:
 - TBD: mach5 tiers 1-5

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Commit messages:
 - 8378194: Protect process_pending_interp_only() work with JvmtiThreadState_lock

Changes: https://git.openjdk.org/jdk/pull/29800/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29800&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378194
  Stats: 12 lines in 3 files changed: 8 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/29800.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29800/head:pull/29800

PR: https://git.openjdk.org/jdk/pull/29800