[in progress] Abilities API: Add a core/settings ability

[jorgefilipecosta]

Part of: WordPress/ai#40

Summary

Adds a read-only core/settings ability to the Abilities API. It returns WordPress settings — those flagged with a new show_in_abilities registration arg — as a flat name => value map, with per-setting metadata (type, title, description, default) carried in the output schema. Callers can filter by settings group or by slugs (mutually exclusive). Requires manage_options.

This is a flat-output alternative to #10747. The logic lives in a new internal WP_Settings_Abilities class (src/wp-includes/abilities/class-wp-settings-abilities.php), structured so a future core/manage-settings write ability can reuse its helpers (get_exposed_settings(), value_schema(), cast_value()).

Test plan

In wp-admin, open the browser console:

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

await executeAbility( 'core/settings', {} );                       // all exposed settings
await executeAbility( 'core/settings', { group: 'reading' } );     // one group
await executeAbility( 'core/settings', { slugs: [ 'blogname' ] } ); // specific names

• Returns a flat name => value map with typed values (e.g. posts_per_page is an int, use_smilies a bool)
• group and slugs filters narrow the result; supplying both at once is rejected
• A non-admin user (no manage_options) is denied

PHPUnit coverage added in tests/phpunit/tests/abilities-api/wpRegisterCoreSettingsAbility.php.

[github-actions]

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Props jorgefilipecosta, justlevine.

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[github-actions]

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[justlevine]

@jorgefilipecosta can you link this to the trac ticket please? I don't have edit perms in this repo.
https://core.trac.wordpress.org/ticket/64605