Fix: Allow dropping blocks into blocks with button block appender

[gziolo]

Description

With the recent addition of the button block appender for Column and Group blocks it's no longer possible to drag a block when there is appender displayed. To work around it, you have to add any block using the appender first. This PR fixes it.

How has this been tested?

Add both Column and Group block to the existing post. Try to drag and drop any block and observer the block button appender being replaced with the selected block.

Screenshots

This is how it works with changes applied:

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[aduth]

I think this is an improvement, and a trivial change at that, so I'd agree to merge it as is.

That being said, I think it would be worth exploring design enhancements in the future which consider treating the entire button area as a droppable target. At least, that was my first intuition, and it was not obvious to me to need to place the cursor at the top edge of the button.

[kjellr]

Tested, and this works for me too. 🎉

I agree, it would be cool to allow people do drag + drop on the actual appender itself as a later iteration. We could borrow the blue dropzone treatment we use elsewhere when the item is being dropped on the appender.

[gziolo]

Yes, this seems like a great improvement to use the whole area of the button. I will explore it further in a follow-up PR. I did a quick test earlier today with wrapping the button with the drop zone component but it didn’t work. I will try different approach.

[mapk]

Excellent! Dragging and dropping on the appender itself would be awesome! I feel that would be a step in the right direction toward this: #13202

[getdave]

@gziolo Glad this was a simple as I thought! 👍 Sorry for missing it first time around.