RFR: 8374876: Epsilon: Convert to use Atomic<T>

[Aleksey Shipilev]

Epsilon uses AtomicAccess on volatile data. Convert it to use Atomic<T>. 

Additional testing:
 - [x] Linux x86_64 server fastdebug, `gc/epsilon`, 100x

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Commit messages:
 - Atomics

Changes: https://git.openjdk.org/jdk/pull/29163/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29163&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374876
  Stats: 14 lines in 4 files changed: 2 ins; 3 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/29163.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29163/head:pull/29163

PR: https://git.openjdk.org/jdk/pull/29163