Twenty Nineteen: Add padding for full-aligned text blocks inside of a full-width column block.

[kjellr]

As noted by @dianeco, after #46999, text-based blocks inside of a full-width columns block now bump up against the edges of the screen:

In the case of media/image blocks, it's likely that users will want these to bump right up against the edge of the page, so we should try adding some padding only to text-based blocks if possible.

Note that this needs to be fixed in both the editor and front-end.

[kjellr]

Noting that there's a somewhat related bug in the editor right now:

​https://github.com/WordPress/gutenberg/issues/15192

When a column block is set to be fullscreen, The block toolbar for nested blocks is pushed off-screen on the left. Not sure if there is also some block padding that's being pushed off-screen.

[ianbelanger]

Adds padding to all items in column block, except images

[davidbaumwald]

This ticket hasn't seen any movement this cycle. With 5.3 RC1 approaching, this is being moved to Future Release. If a committer feels strongly about this one being in 5.3 and has the time to see it through, it can be moved back up.