[jdk24] RFR: 8345423: Shenandoah: Parallelize concurrent cleanup

[Xiaolong Peng]

Clean backport, improve performance of concurrent cleanup of Shenandoah and GenShen, remove the use of heap lock from concurrent cleanup.

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Commit messages:
 - Backport 4da6fd4283a13be1711e7ad948f1d05a0a9148a5

Changes: https://git.openjdk.org/jdk/pull/22991/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22991&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345423
  Stats: 228 lines in 13 files changed: 79 ins; 56 del; 93 mod
  Patch: https://git.openjdk.org/jdk/pull/22991.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22991/head:pull/22991

PR: https://git.openjdk.org/jdk/pull/22991