Instead of using "box" layouts for these import/export operators, use
panels instead.
Motivation for doing so is two fold.
Firstly the use of panels instead of boxes is more consistent with other
parts of Blender and with other IO addons implemented in Python (FBX,
glTF, 3ds, etc.)
Secondly, in the case of an Import invoked from drag-n-drop or Export
configured on a Collection, the large number of options often exposed
results in very long layouts. 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.
USD is a bigger change and requires some additional coordination. It
will be submitted and reviewed separately.
Pull Request: https://projects.blender.org/blender/blender/pulls/121557
b773eca1b5