RFR: 8376195: Convert ThreadLocalAllocBuffer to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review the change to use `Atomic<T>` in `ThreadLocalAllocBuffer`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8376195

Changes: https://git.openjdk.org/jdk/pull/29386/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29386&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376195
  Stats: 28 lines in 4 files changed: 2 ins; 9 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/29386.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29386/head:pull/29386

PR: https://git.openjdk.org/jdk/pull/29386