Block API: Explore how block variations could be embedded in other places

[gziolo]

Description

Follow-up for #16283.

Some ideas were previously shared by @kjellr in #16283 (comment):

In many cases, it'll make sense to include these options in the setup state. Beyond that, they'll likely also need to live in either the Block Switcher menu, or in the Sidebar:

Layout Options in the Sidebar:

Layout Options in the Block Switcher:

[ocean90]

It would be nice to have at least one of the options since it doesn't seem to be possible to use transforms to switch to another variation due to the same block name.

[paaljoachim]

It seems this issue is very much associated:
#20583

---

Suggestion that we add a new Layout sidebar panel.

Layout is the top level in a Block. As it has to do with how the block elements are laid out.
Styles is the styling of the elements inside the Block.
Today styles and layouts are somewhat mixed together in one panel.

A figma example with the Columns Block: (We can also switch out the word variation with layout.)

Mini prototype.
https://www.figma.com/proto/HcOy92XlgMNtUjH5KF2Os0/New-Sidebar-Layout-Panel?node-id=2%3A0&scaling=min-zoom

Examples where a Layout panel would be good to have:
Columns.
Media & Text.
Buttons Block, Navigation Block and Social Icons Block - horizontal/vertical layout.
and probably other blocks as well.

[ntsekouras]

This shouldn't be coupled with styles and layout in mind because there are blocks that just change attributes and nothing else visually, like the embed block.

Related issue: #25231

[gziolo]

I think we can close it in favor of #25231 that is covering exactly the same topic.