RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen [v4]

[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 incrementally with one additional commit since the last revision:

  Resolve merge conflicts

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files/7038d0a5..ce8058f1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=03
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=02-03

  Stats: 55 lines in 2 files changed: 17 ins; 30 del; 8 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