The code that restored collection flags after they are rebuilt when
moving a collection didn't take into account collection children. The
flag for the active collection was properly restored, but all of its
children would take on the exclude flag of the collection the active
collection was dragged into.
This commit builds a temporary tree structure to store the flags for
the moving collection and its children. Then it reapplies these flags
after `BKE_main_collection_sync`.
Differential Revision: https://developer.blender.org/D9158
Hans Goudey
89491d67d9