RFR: 8306027: Clarify JVMTI heap functions spec about virtual thread stack.

Tue Apr 25 22:30:41 UTC 2023

The fix updates JVMTI spec updates description of heap functions to support virtual threads.
Virtual threads are not heap roots by design, so FollowReference/IterateOverReachableObjects specs are updated to note only platform threads.
References from thread stacks (including virtual threads) are reported as JVMTI_HEAP_REFERENCE_STACK_LOCAL/JVMTI_HEAP_REFERENCE_JNI_LOCAL, so description of the values is relaxed.

Also please review related CSR

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Commit messages:
 - spec update

Changes: https://git.openjdk.org/jdk/pull/13661/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13661&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306027
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/13661.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13661/head:pull/13661

PR: https://git.openjdk.org/jdk/pull/13661