RFR: 8378194: Protect process_pending_interp_only() work with JvmtiThreadState_lock [v2]

[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

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

  review: add two asserts; load/store _pending_interp_only_mode atomically

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29800/files
  - new: https://git.openjdk.org/jdk/pull/29800/files/edaa43e9..8a626c1e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29800&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29800&range=00-01

  Stats: 8 lines in 2 files changed: 5 ins; 0 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