RFR: 8375624: G1: Convert G1JavaThreadsListClaimer to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change that makes `G1JavaThreadsListClaimer` use `Atomic<T>` instead of `AtomicAccess'.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8375624

Changes: https://git.openjdk.org/jdk/pull/29299/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29299&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375624
  Stats: 7 lines in 2 files changed: 1 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/29299.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29299/head:pull/29299

PR: https://git.openjdk.org/jdk/pull/29299