[lilliput-jdk21u:lilliput] RFR: 8315046: [Lilliput/JDK21] Cherry-pick: 8305896: Alternative full GC forwarding [v2]

[Roman Kennke]

> Let's cherry-pick the alternative full GC forwarding PR in its current state into Lilliput-21.
> I needed to make some adjustments because PreservedMarks stuff has been refactored between 21 and 22.
> 
> Testing:
> - [ ] hotspot_gc +UseAltGCForwarding
> - [ ] hotspot_gc -UseAltGCForwarding

Roman Kennke 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 branch 'lilliput' into JDK-8315046
 - 8315046: [Lilliput/JDK21] Cherry-pick: 8305896: Alternative full GC forwarding

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

Changes:
  - all: https://git.openjdk.org/lilliput-jdk21u/pull/3/files
  - new: https://git.openjdk.org/lilliput-jdk21u/pull/3/files/fd29cbb7..7e4e993f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=3&range=01
 - incr: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=3&range=00-01

  Stats: 399 lines in 15 files changed: 349 ins; 33 del; 17 mod
  Patch: https://git.openjdk.org/lilliput-jdk21u/pull/3.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk21u.git pull/3/head:pull/3

PR: https://git.openjdk.org/lilliput-jdk21u/pull/3