[jdk19] RFR: 8289439: Clarify relationship between ThreadStart/ThreadEnd and can_support_virtual_threads capability

[Alan Bateman]

The description of the ThreadStart/End events in the JVM TI spec needs rewording to make it clearer when these events are sent for virtual threads and when VirtualThreadXXX events are sent instead.

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Commit messages:
 - Tweak wording
 - Initial commit

Changes: https://git.openjdk.org/jdk19/pull/94/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19&pr=94&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289439
  Stats: 29 lines in 2 files changed: 12 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk19/pull/94.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/94/head:pull/94

PR: https://git.openjdk.org/jdk19/pull/94