Support additional link types in navigation item creation

[jeryj]

The Extensible Site Editor Sidebar should support more link types when creating navigation items. This would make Navigation List View a more complete editing surface for common menu-management tasks.

This will also improve the general link creation experience. At the moment, to create a Category from a Navigation Block you need to:

• Click Navigation Block Appender
• Link Control opens with search focused
• Know to click "Add Block"
• Click "Category" or the full block inserter and search "Category"
• Brings you back to the Link Control Search
• Type category you want
• ...

We should remove the limitation to only return pages from the link control. The Link Control should work like the inline link selection (adding a link to paragraph content, for example). This would make the flow:

• Click Navigation Block Appender
• Link Control opens with search focused
• • Type category you want
• ...

To complete this issue, we'd need to:

• Return all results from Link Control Search
• Prioritize Page results
• Show link type in the search results
• Possible: Do we need to remove type blocks and rely just on Navigation Link Block? I.e. Category, Post, Page, etc and return to one Navigation Link block? This would be a big lift, I fear, and could cause back compat issues if a block is removed. I can see how having "Category" or "Page" in the block inspector sidebar is quite helpful, so maybe this is best left alone.