RFR: 8375616: G1: Convert G1BatchedTask to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review the use of `Atomic<T>` for the `G1BatchedTask` class.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8375616

Changes: https://git.openjdk.org/jdk/pull/29321/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29321&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375616
  Stats: 8 lines in 2 files changed: 1 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/29321.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29321/head:pull/29321

PR: https://git.openjdk.org/jdk/pull/29321