RFR: 8351444: Shenandoah: Class Unloading may encounter recycled oops

[William Kemper]

Not clean, but not hard to resolve.

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

Commit messages:
 - Backport cdf7632f8a85611077a27c91ad928ed8ea116f95

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/177/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=177&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351444
  Stats: 52 lines in 4 files changed: 38 ins; 7 del; 7 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/177.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/177/head:pull/177

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/177