RFR: JDK-8313796: AsyncGetCallTrace crash on unreadable interpreter method pointer

[Richard Startin]

Makes AsyncGetCallTrace more resilient to method unloading.

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Commit messages:
 - JDK-8313796: AsyncGetCallTrace crash on unreadable interpreter method pointer

Changes: https://git.openjdk.org/jdk/pull/15193/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313796
  Stats: 45 lines in 5 files changed: 39 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/15193.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15193/head:pull/15193

PR: https://git.openjdk.org/jdk/pull/15193