[N/A] Implement Navigation Slug Reference for Navigation Block

[bd-viget]

Summary

This PR adds a feature to the core Navigation block that tracks the navigation menu's slug in the block attributes in order to keep menus with the same name, but different IDs, in sync across multiple environments (local, staging, production, etc.).

You should now see a refSlug attribute in the core Navigation menu attributes/JSON which stores the menu's slug (post_name).

Issues

• N/A

Testing Instructions

1. Create/update a template part/pattern and use the core Navigation block.
2. Save the template/pattern changes to the theme (either with the Create Block Theme plugin, or manually by copy/pasting the blocks)
3. Use a separate environment to create menus (they need to have different IDs to correctly test)
4. The corresponding navigation menu should display when the Menu Names match, regardless if the IDs match.

[nathan-schmidt-viget]

LGTM, this will be really nice!!!