RFR: 8359870: JVM crashes in AccessInternal::PostRuntimeDispatch [v6]

[Kevin Walls]

> ThreadDumper/ThreadSnapshot need to handle a failure to resolve the native VM JavaThread from a java.lang.Thread.  This is hard to reproduce but a thread that has since terminated can provoke a crash.  Recognise this and return a null ThreadSnapshot.

Kevin Walls has updated the pull request incrementally with one additional commit since the last revision:

  Test requires: permit linux debug testing

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25958/files
  - new: https://git.openjdk.org/jdk/pull/25958/files/d8143785..d14f5228

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25958&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25958&range=04-05

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25958.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25958/head:pull/25958

PR: https://git.openjdk.org/jdk/pull/25958