Forms: multi page Forms

[simison]

We should support a form flow that focuses on steps. But we should not clutter the semantic space of “pages”; instead we should find a smooth way of representing multi-step forms as a “focused type”, easy to toggle on or off. Formality, while a bit clunky, has some interesting ideas there.

Internal ref p1HpG7-l0G-p2

In our discussions with Team 51 (peKye1-1jj-p2 a) and while doing competitor reviews, we've found out how important multi page forms are for advanced use cases (i.e. other than just basic contact forms).

Multi page forms seem to fill the need that more complex "conversational forms" typically fill, so this should likely be prioritised higher than those.

We should explore the block interactivity API for this purpose.