RFR: 8375974: G1: Convert G1FullCollector to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change to convert `G1FullCollector` to use `Atomic<T>`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8375974

Changes: https://git.openjdk.org/jdk/pull/29342/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29342&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375974
  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/29342.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29342/head:pull/29342

PR: https://git.openjdk.org/jdk/pull/29342