RFR: 8369433: G1: Replace G1MarkScope with NMethodMarkingScope

[duke]

On Wed, 8 Oct 2025 15:39:19 GMT, Francesco Andreuzzi <fandreuzzi at openjdk.org> wrote:

> Replacing `G1MarkScope` with `NMethodMarkingScope`, since they have equivalent implementations.
> 
> Passes tier1 and tier2 (fastdebug).

@fandreuz 
Your change (at version bec19980935dd9790e5ffb96808a0864d547c994) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/27697#issuecomment-3385667344