RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen [v6]

[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 pull request now contains seven commits:

 - Merge remote-tracking branch 'gitfarm/backport-kdnilsen-9d2712dd-master-gh' into backport-kdnilsen-9d2712dd-master
 - Merge remote-tracking branch 'origin/master' into backport-kdnilsen-9d2712dd-master-gh
 - Revert incorrect resolution of merge conflict
   
   One of the changes recently committed in attempt to resolve merge
   conflict was wrong.
 - Resolve merge conflicts
 - TestAllocIntArrays sometimes fails with aggressive heuristics
   
   This bug has been fixed in TIP.  The fix was not backported to JDK21.
 - Merge remote-tracking branch 'origin/master' into backport-kdnilsen-9d2712dd-master
 - Backport 9d2712ddf39160a618c9c839c46d2510063f45df

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

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/62/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=62&range=05
  Stats: 2389 lines in 21 files changed: 1500 ins; 255 del; 634 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