RFR: 8369980: Use ThreadsClaimTokenScope in ShenandoahThreadRoots

[William Kemper]

On Thu, 16 Oct 2025 11:02:50 GMT, Francesco Andreuzzi <fandreuzzi at openjdk.org> wrote:

> The explicit usage of `Threads::change_thread_claim_token` and `Threads::assert_all_threads_claimed` in `ShenandoahThreadRoots` can be replaced with `ThreadsClaimTokenScope`.
> 
> Passes tier1, tier2, tier[1,2,3]_gc_shenandoah (fastdebug).

Looks good to me.

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Marked as reviewed by wkemper (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27845#pullrequestreview-3346499018