RFR: 8368989: Use NMethodMarkingScope and ThreadsClaimTokenScope in shenandoahSTWMark

[duke]

On Wed, 1 Oct 2025 08:57:07 GMT, Francesco Andreuzzi <fandreuzzi at openjdk.org> wrote:

> Replace `StrongRootsScope` with `ThreadsClaimTokenScope` in `shenandoahSTWMark` to be more precise with what is needed and why. 
> 
> - `ShenandoahSTWMark` uses `MarkingNMethodClosure`, so we also need `NMethodMarkingScope`.
> - `nworkers` is guaranteed to be > 0
> 
> Passes `tier1` and `tier2` (fastdebug).

@fandreuz 
Your change (at version 442bc5be6ca713c7fcabf8a0ad87f74f97d58181) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/27589#issuecomment-3359879615