RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen [v2]

[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.

Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into backport-kdnilsen-9d2712dd-master
 - Backport 9d2712ddf39160a618c9c839c46d2510063f45df

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files/7237da32..5b6a8543

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=00-01

  Stats: 38 lines in 3 files changed: 26 ins; 7 del; 5 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