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

[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

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Commit messages:
 - 8315046: [Lilliput/JDK21] Cherry-pick: 8305896: Alternative full GC forwarding

Changes: https://git.openjdk.org/lilliput-jdk21u/pull/3/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=3&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315046
  Stats: 1196 lines in 39 files changed: 1077 ins; 10 del; 109 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