RFR: 8341099: GenShen: assert(HAS_FWD == _heap->has_forwarded_objects()) failed: Forwarded object status is sane

[William Kemper]

Clean backport

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Commit messages:
 - Backport cbc0fd0a2aae095c7fda3d69a113bf504ffef594

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/118/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=118&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341099
  Stats: 10 lines in 1 file changed: 8 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/118.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/118/head:pull/118

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/118