RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen [v5]

[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:

  Revert incorrect resolution of merge conflict
  
  One of the changes recently committed in attempt to resolve merge
  conflict was wrong.

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

Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files/ce8058f1..9ecc1914

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=04
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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