RFR: 8294924: JvmtiExport::post_exception_throw() doesn't deal well with concurrent stack processing [v2]

[Erik Österlund]

> There is a stack walk in JvmtiExport::post_exception_throw() that has safepoints in it. This trips up the stack watermark code. This patch adds a RAII object to JvmtiExport::post_exception_throw() that keeps the thread and its stack fully processed throughout the function.
> Testing: tier1-7 of ZGC tests on linux x86_64 debug and manual testing of the test that failed.

Erik Österlund has updated the pull request incrementally with one additional commit since the last revision:

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11238/files
  - new: https://git.openjdk.org/jdk/pull/11238/files/6aabc24b..f59ead1b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11238&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11238&range=00-01

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11238.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11238/head:pull/11238

PR: https://git.openjdk.org/jdk/pull/11238