RFR: 8350285: Shenandoah: Regression caused by ShenandoahLock under extreme contention

[William Kemper]

Clean backport

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Commit messages:
 - Backport bd8ad309b59bceb3073a8d6411cca74e73508885

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/167/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=167&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350285
  Stats: 18 lines in 2 files changed: 15 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/167.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/167/head:pull/167

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/167