Navigation: Add block search and insertion from Link UI

[sarthaknagoshe2002]

What?

Closes #77074

This PR enables users to search for and insert allowed inner blocks (such as Site Logo, Search, or Home link) directly from the Navigation block's Link UI popover.

Why?

Previously, adding inner blocks to the Navigation block required a separate workflow from adding standard links. By integrating block search into the Link UI, we streamline the user experience.

How?

Uses useSelect to gather all available block types and check their insertion permissions. It then filters this list in real-time based on the user's search input and whether the blocks are actually allowed within the Navigation menu. Finally, it passes these matching blocks down into the LinkUITools component, which loops through the results to display clickable insertion buttons for the user.

Testing Instructions

1. Hover over navigation block to get the "+" appender icon.
2. Click on the "+" to open the Link UI popover.
3. Type "Home" into the focused search input field.
4. Verify the relevant block appear in the list.

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: sarthaknagoshe2002 <sarthaknagoshe2002@git.wordpress.org>
Co-authored-by: jeryj <jeryj@git.wordpress.org>

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