Navigation: Add new block-based screen to Customizer

[noisysocks]

Should we replace Appearance → Customizer → Menus with a slimmed down version of the Navigation editor?

This would match what the new block-based Widgets editor does.

	WP Admin	Customizer
Widgets
Navigation		What goes here?

[shaunandrews]

I think it could make sense, but its unclear to me if this is a priority.

[celloexpressions]

If #26012 goes in the direction of consolidating widgets into the customizer, we should strongly consider doing the same for menus. If it's a separate interface, we should make sure that menu management in the customizer and elsewhere is cross compatible.

The current menu management in the customizer works well in the sidebar. The ability to draft pages while building out a menu is extremely powerful. And we should probably maintain a slide-out UI for adding menu items.

[Thelmachido]

Closing this issue due to the Navigation Editor project being moved to an inactive status on the feature projects page in coordination with the project leads. At the moment we have the navigation block, if this work is picked back up, issues can be revisited and reopened as needed.