[jdk21u-dev] RFR: 8279016: JFR Leak Profiler is broken with Shenandoah

[Aleksey Shipilev]

Plugs the bug opportunity with Shenandoah and JFR. Both changes apply cleanly, and both are need at the same time to keep the tests clean.

Additional testing:
 - [x] MacOS AArch64 fastdebug, `jdk_jfr`
 - [x] MacOS AArch64 fastdebug, `jdk_jfr` with `-XX:+UseShenandoahGC`

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Commit messages:
 - Backport 0c281acfb4c87436096cb562d70f800dffa3671a
 - Backport 0be7118b2f761b416ebf8cbb11473d51e80be409

Changes: https://git.openjdk.org/jdk21u-dev/pull/1439/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1439&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8279016
  Stats: 81 lines in 5 files changed: 81 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1439.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1439/head:pull/1439

PR: https://git.openjdk.org/jdk21u-dev/pull/1439