Instead of using "box" layouts for these import/export operators, use
panels instead. Many choices for the layout and organization has come
from the `universal-scene-description` branch though it's not a 1:1
equivalent.
Motivation for using panels is two fold.
Firstly the use of panels instead of boxes is more consistent with other
parts of Blender and with the other IO features.
Secondly, in the case of an Import invoked from drag-n-drop or Export
configured on a Collection, the large number of options exposed results
in a very long layout. Panels allow us to close some sections by default
and allows the user to open/close panels based on their own needs in
general.
Along the way some effort went into standardizing the layout and wording
used as much as possible.
Pull Request: https://projects.blender.org/blender/blender/pulls/122415
06581bde1b