New Onboarding: Improve design preview layout

[lsl]

#49170 introduced landscape design previews for onboarding's /new/designs. @simison noticed that the spacing between designs and size of the images displayed at different breakpoints could use some debugging to avoid tiny images in some situations.

What we need:

Images to be legible at as many breakpoints as possible

How:

I suspect you'll need a mix of both reworking breakpoints, and reducing the column gap size.

Why:

At some breakpoints the design previews become very small where as they eventually snap larger at a smaller breakpoint with less columns. It isn't possible to remove this effect completely but currently images get way too small to be reasonable, we'd like them to jump to the larger size / less columns sooner.

Screen.Recording.2021-01-26.at.13.05.57.480p.mov