Experiments with another Form API

So some time passed, and I've come to like the new components for the Form. Our needs have grown as well, though, and the ergonomics of the Form API are not ideal so far, especially when it comes to FormRowOffset. Thus I've experimented with a slightly better API, with fewer caveats, and more straightforward to use.

To all who've played with the new Form components, how do you like it? Do you prefer the former or newer variants? Is there anything you'd modify or that you'd think would be a nice addition?

If there's no problem with this new approach, I think we could remove the older FormRow / FormRowOffset components with this MR. There's another MR in flight that uses those, but the migration path is pretty straightforward and I don't envision any difficulties migrating to this new scheme.