RFR: 8375971: G1: Convert G1EvacStats. to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change that moves `G1EvacStats` to use `Atomic<T>`.

Testing: gha

Thanks,
  Thomas

-------------

Commit messages:
 - 8375971

Changes: https://git.openjdk.org/jdk/pull/29341/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29341&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375971
  Stats: 67 lines in 3 files changed: 24 ins; 9 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/29341.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29341/head:pull/29341

PR: https://git.openjdk.org/jdk/pull/29341