Duplicating collection doesn't work when multiple collections are
selected, instead first selected collection is just duplicated. Now fixed
by iterating over list of selected collections returned by
`outliner_collect_selected_parent_collections` after traversing. In that
function, child collections are skipped if parent collection is already
selected, this avoids extra copies from being generated (i.e creates one
copy of nested collections).
Resolves#139651
Pull Request: https://projects.blender.org/blender/blender/pulls/139719
e24f46b12b