Navigation Screen: Remove List View and display vertical Navigation variant

[shaunandrews]

The current Navigation screen shows a horizontal Navigation block alongside the List View. Essentially, this displays the same things twice, and the only discernible difference is that one is a horizontal list and the other is a vertical list.

I think it might make more sense to remove the List View (maybe bringing it back as a popover or optional sidebar) and default to showing the Navigation block's vertical variant.

[MarvelMoe]

I agree that it should be an optional view ... if you have a few menu items it might not be needed. But it comes in handy when you have a large amount of sub menu items and want them expanded by default. See screenshot for example:

[talldan]

This was done in #28675