[lilliput-jdk21u:lilliput] RFR: 8316108: [Lilliput/JDK21] Cherry-pick: 8305898: Alternative self-forwarding mechanism

[Roman Kennke]

Let's cherry-pick the current state of the upstream PR https://github.com/openjdk/jdk/pull/13779. It applies cleanly on top of lilliput/jdk21u.

Testing:
 - [ ] hotspot_gc (+UseAltGCForwarding)
 - [ ] hotspot_gc (-UseAltGCForwarding)

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Commit messages:
 - 8316108: [Lilliput/JDK21] Cherry-pick: 8305898: Alternative self-forwarding mechanism

Changes: https://git.openjdk.org/lilliput-jdk21u/pull/4/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=4&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316108
  Stats: 101 lines in 8 files changed: 85 ins; 2 del; 14 mod
  Patch: https://git.openjdk.org/lilliput-jdk21u/pull/4.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk21u.git pull/4/head:pull/4

PR: https://git.openjdk.org/lilliput-jdk21u/pull/4