RFR: 8374684: ZGC: Convert zMark to use Atomic<T>

[Thomas Schatzl]

On Thu, 15 Jan 2026 06:09:25 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> Convert usages of AtomicAccess to Atomic<T> in zMark.
> 
> Testing:
>  * GHA
>  * HotSpot GC tests with ZGC linux x64 and linux aarch64

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29245#pullrequestreview-3686390068