RFR: 8377126: Shenandoah: Convert ShenandoahVerifier related code to use Atomic<T> [v2]

[Aleksey Shipilev]

On Thu, 5 Feb 2026 16:54:34 GMT, Ben Taylor <btaylor at openjdk.org> wrote:

>> Modernizes ShenandoahVerifier code by replacing `AtomicAccess` methods with `Atomic<T>` types.
>> 
>> Tier1 test results on x86_64 linux are the same before and after this change when running with `TEST_VM_OPTS=-XX:+UseShenandoahGC`.
>
> Ben Taylor has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Restore dropped  in shenandoahVerifier

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29576#pullrequestreview-3758424642