[jdk20u] RFR: 8305403: Shenandoah evacuation workers may deadlock

[William Kemper]

Clean backport of:
>8305403: Shenandoah evacuation workers may deadlock
>Reviewed-by: rkennke, ysr

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Commit messages:
 - Backport 793da60ee833d09db0f6f14b50a7cbd7f4549e3b

Changes: https://git.openjdk.org/jdk20u/pull/65/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk20u&pr=65&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305403
  Stats: 39 lines in 6 files changed: 1 ins; 33 del; 5 mod
  Patch: https://git.openjdk.org/jdk20u/pull/65.diff
  Fetch: git fetch https://git.openjdk.org/jdk20u.git pull/65/head:pull/65

PR: https://git.openjdk.org/jdk20u/pull/65