What?

Closes #76805

This PR introduces a parallel slug-based lookup to __experimentalFetchLinkSuggestions when a user searches for content. It bypasses the limitation where the core /wp/v2/search endpoint strictly screens text matches against titles and excerpts, entirely leaving out valid matches containing different URL slugs.

Why?

When managing slugs & special character routing (e.g., changing a slug from kursuebersicht to kurse while maintaining the presentation title as Kursübersicht), users inevitably search for pages by their URL paths/slugs inside the Link UI popover.

Because /wp/v2/search completely disregards slug criteria, it yields empty payloads for those keywords. There are zero client-side results available to filter or sort.

How?

• Implemented sub-queries inside the main link search queue to query content types directly by the exact slug keyword.
• Introduced targeted fallback requests directly to the content type routes (/wp/v2/posts or /wp/v2/pages) via the slug= argument, extract hidden records & deduplicate them against title matches.
• Refactored the sortResults calculator by parsing slugs with a clean extractSlug helper and assigning a specialized exact slug scale coefficient (8). This slots slug matching elegantly right beneath an exact title match (10) but completely above fuzzy or string-token fraction overlaps (<1).

Scenario Setup

Create three separate pages in your WordPress dashboard with distinct titles and slugs to test both exact slug matches and fuzzy title matches:

• Page 1 (Target Page): Title: Kursübersicht | Slug: kurse (The word "kurse" is only in the slug and completely absent from the title).
• Page 2 (Distractor Page): Title: Advanced Course Material | Slug: advanced-training (The title contains a partial semantic match for the query).
• Page 3 (Noise Page): Title: Contact Us | Slug: contact | Body Content: "If you have questions about our Kurse, let us know!"

Testing Instructions

1. Open any post or page for editing, highlight some text, open the link selection wrapper.
2. Input the exact string kurse into the search field.
3. Observe the resulting dropdown options.
4. The page titled Kursübersicht must be successfully pulled into the results list via the new parallel slug lookup path and float to the absolute top of the list due to its exact slug score modifier. It should be followed secondarily by content match (Contact Us), proving that the exact slug match successfully outranks standard fuzzy content matches.

Screenshots or screencast

Before	After