Inconsistent placeholder/start states between Group and Columns blocks

[richtabor]

We currently have two different looks for similar placeholder states, between the Group and Columns block. Is there a reason we should have two varying states here? If not, we should move these states closer together:

[richtabor]

Noted that you also can't drop in blocks to the Group block's placeholder state in the content area.

And we may be able to reduce this back to the simpler "empty" Group block state, by adding these as top-level toolbar controls in some fashion via #49524

[richtabor]

Noted that you also can't drop in blocks to the Group block's placeholder state in the content area.

Actually, you can drop in blocks, there's just no indicator that it's possible (#39064).

[jasmussen]

What do you say we merge these two to be the same? (In the style of the former). Conceptually, the group can be the starting point for a variety of different layouts.

The main challenge is how a columns block behaves differently from, for example, a row block. But this is already an issue given we have the multiple options to create columns, and multiple setup states. Ideally merging the two into one — same state for both blocks — could be a way to explain the differences perhaps.