RNA pointers should always have valid owner IDs. And most structs
using STRUCT_UNDO do not need it because the owner is a UI datablock
which already determines if undo is needed.
With this change, it is possible to have structs used both in UI and scene
datablocks and have undo work depending on the owner. This is needed for
collections storing operator properties for export (#116646).
Pull Request: https://projects.blender.org/blender/blender/pulls/117640
2b0caf00a8