RFR: JDK-8313796: AsyncGetCallTrace crash on unreadable interpreter method pointer [v3]

[Richard Startin]

> Makes AsyncGetCallTrace more resilient to method unloading.

Richard Startin has updated the pull request incrementally with three additional commits since the last revision:

 - revert unnecessary whitespace changes
 - revert yet another unnecessary change
 - revert unnecessary change

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15193/files
  - new: https://git.openjdk.org/jdk/pull/15193/files/6a257d4b..86813482

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15193&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15193&range=01-02

  Stats: 5 lines in 2 files changed: 3 ins; 1 del; 1 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