Add a core/settings ability

[jorgefilipecosta]

Summary

Adds the core/settings ability to the plugin, matching the equivalent WordPress core change in WordPress/wordpress-develop#12141. Read-only; returns settings flagged show_in_abilities as a flat name => value map (metadata in the output schema), filterable by group or slugs (mutually exclusive). Requires manage_options.

• Settings — registers core/settings. Kept near-identical to core's WP_Settings_Abilities (differences marked with // Plugin: comments). It registers at priority 11 and unregisters any core-provided copy first, so the plugin's version wins when both are present.
• Show_In_Abilities — seeds the show_in_abilities flag onto a curated set of core settings via the register_setting_args filter, so the ability returns data on a stock site before core ships the flag. Object-type-agnostic, for future reuse (post types, meta).

Test plan

In wp-admin, open the browser console:

const { executeAbility } = await import( '@wordpress/abilities' );

await executeAbility( 'core/settings', {} );
await executeAbility( 'core/settings', { group: 'reading' } );
await executeAbility( 'core/settings', { slugs: [ 'blogname' ] } );

• Flat name => value map with typed values
• group / slugs filters work; supplying both is rejected
• Non-admin (no manage_options) is denied

Integration tests added under tests/Integration/Includes/Abilities/.

[github-actions]

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Co-authored-by: jorgefilipecosta <jorgefilipecosta@git.wordpress.org>

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