RFR: 8336944: Shenandoah: Should only relativize stack chunks for successful evacuations

[William Kemper]

In some cases, different threads may race to evacuate an object. The race is won by "CAS"ing in the forwarding pointer. The threads that lose this race must "back out" their allocation. The work to relativize stack chunks should only happen for the thread that wins the evacuation race.

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Commit messages:
 - Only relativize stack chunks for the evacuated object that wins the race

Changes: https://git.openjdk.org/jdk/pull/20288/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20288&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336944
  Stats: 3 lines in 1 file changed: 1 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20288.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20288/head:pull/20288

PR: https://git.openjdk.org/jdk/pull/20288