RFR: 8376115: G1: Convert G1CMRootRegions to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change to convert `G1CMRootRegions` to use `Atomic<T>`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8376115

Changes: https://git.openjdk.org/jdk/pull/29363/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29363&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376115
  Stats: 21 lines in 2 files changed: 0 ins; 0 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/29363.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29363/head:pull/29363

PR: https://git.openjdk.org/jdk/pull/29363