#14439 fix: filter associated nav menu items by menu

[skikken]

Changes:

1. Adds a new optional $menu_id parameter (default 0, appended after $taxonomy so all existing calls are unaffected). When set, only menu items belonging to that menu are returned.
2. Validates the menu ID up front: if a non-zero $menu_id does not correspond to an existing nav_menu term, the function returns an empty array. This covers the invalid-ID case from the 2015 refresh.
3. Filters by the item's nav_menu term assignment (wp_get_post_terms()) inside the existing loop, so the query shape is unchanged and behavior for the existing object types is identical.

Backward compatibility is preserved: calls without $menu_id return items from all menus exactly as before, which the included unit test asserts explicitly.

Trac ticket: https://core.trac.wordpress.org/ticket/14439

Use of AI Tools

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Tool(s): Claude
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[github-actions]

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