Fix up spacing for ListEditWidget instances.
Review Request #12595 — Created Sept. 13, 2022 and submitted
The list edit widget that we use for some complex form fields didn't
have proper spacing, ending up with everything all smushed together.
This change adds some margins so that things look nice(r).
Looked at the diffviewer settings and OAuth application form where we
use this widget in a couple different ways. Saw that things looked nicer
Lookin' good, thanks for adding that!