RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen

[Kelvin Nilsen]

This pull request contains a backport of commit 9d2712dd from the openjdk/shenandoah repository.

The commit being backported was authored by Kelvin Nilsen on 26 Jun 2024 and was reviewed by William Kemper and Y. Srinivas Ramakrishna.

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Commit messages:
 - Backport 9d2712ddf39160a618c9c839c46d2510063f45df

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327000
  Stats: 2425 lines in 22 files changed: 1531 ins; 263 del; 631 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/62.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/62/head:pull/62

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/62