Add blockGap as a default control on Columns/Column blocks

[richtabor]

What?

The Group block has padding and blockGap as default controls. The Columns and Column blocks should have those same controls enabled by default, as they are very similar to the Group block.

Why?

Consistency. I would expect the similar blocks to have similar experiences right off.

How?

Adding support via the core/columns block.json.

Testing Instructions

1. Open a Post or Page.
2. Insert a Columns block.
3. Open Block Inspector.
4. See "Block Spacing" as a default option in the "Dimensions" panel.
5. Repeat steps 2-4 for the Column block.

Screenshots or screencast

Before (Column block is the same):

After (Column block is the same):

[paaljoachim]

Thanks for adding the Block Spacing control to the Columns block, Rich!

Using WordPress 6.2
Theme: Twenty Twenty Three
Browser: Brave

Before:

After:
Using the PR Gutenberg build.

Testing.
Set Black Spacing to 0 in the parent Columns.
Added padding to each column.

Frontend.

It works well!

[jameskoster]

It's a bit strange how the default spacing and the control seem contradictory:

But I suppose that's just #43082 rearing it's head once again...

[richtabor]

But I suppose that's just #43082 rearing it's head once again...

Yes indeed. :/

[Marc-pi]

@richtabor seems it covers #41345 that we can close i guess
nice addition, we can build cards now ;-)

[richtabor]

@richtabor seems it covers #41345

Not quite. That is asking for radius to be added to the individual column blocks.

[Marc-pi]

hum, i thought you added on columns also. the recurrent need is to build cards, like for services prices (ex: maintenance packs)
from the screenshots above, radius is available on child Column, no ?
or maybe the issue title brings to confusion ??

[richtabor]

from the screenshots above, radius is available on child Column, no ?

This PR makes blockGap visible right off for Columns/Columns, not radius. The parent Columns block supports radius, but the Column block does not currently.

[paaljoachim]

I noticed a draft PR by Aaron which has stopped up located here:
#40925