Navigation Block: add support for vertical menus

[noisysocks]

Both horizontal (e.g. in a header) and vertical (e.g. in a sidebar) menus should be supported by the Navigation block.

[melchoyce]

As an example, I'm working on designing a theme right now that would benefit from having a vertical menu block:

Currently, there's no way to achieve this using the navigation block without using a bunch of CSS hacks. Native support would be helpful for achieving this kind of menu design in Gutenberg themes.

[mtias]

Agree this should be achievable. It'd be good to explore using this API for it: #16283.

[mtias]

Notice this could be a great case for using the variations system if we want to make it easily discoverable in the inserter.

[paaljoachim]

The question is then how to add a way to make the navigation vertical.
Some options as I see it.
A control in the sidebar to switch the navigation between horizontal/vertical.
A Styles pattern. User selects the vertical pattern.
A narrow alignment option that pushes the navigation to become vertical.

Styles
Adding a styles vertical pattern.

Alignment
Adding a narrow alignment pushing the navigation to become vertical.

[karmatosed]

Notice this could be a great case for using the variations system if we want to make it easily discoverable in the inserter.

@mtias are you suggesting have 2 types of navigation blocks?

[paaljoachim]

Btw here is something similar. "[Enhancement] Added a vertical style to the Buttons block."
#20160 (comment)
It would probably be nice with a common approach.