RFR: 8376351: Parallel: Convert ParallelScavengeHeap to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change to use `Atomic<T>` in `ParallelScavengeHeap`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8376351

Changes: https://git.openjdk.org/jdk/pull/29424/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29424&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376351
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/29424.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29424/head:pull/29424

PR: https://git.openjdk.org/jdk/pull/29424