RFR: 8374690: ZGC: Convert zRelocate to use Atomic<T>

[Axel Boldt-Christmas]

Convert usages of AtomicAccess to Atomic<T> in zRelocate.

Testing:
 * GHA
 * HotSpot GC tests with ZGC linux x64 and linux aarch64

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

Commit messages:
 - ZGC: Convert zRelocate to use Atomic<T>

Changes: https://git.openjdk.org/jdk/pull/29268/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29268&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374690
  Stats: 17 lines in 2 files changed: 1 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/29268.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29268/head:pull/29268

PR: https://git.openjdk.org/jdk/pull/29268