RFR: 8369980: Use ThreadsClaimTokenScope in ShenandoahThreadRoots

[duke]

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).

@fandreuz 
Your change (at version 42b50e908a49cf3378c36b44ec8c0f66efb5288d) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/27845#issuecomment-3414669462