WorldPartition: Attached Actors within Level Instances save level offset bounds

The proposed fix is implemented in CL 25389340 but needs further testing to make sure there are no issues caused by it.

1. Create World Partition world (save it out)
2. Create a Cube and a Cone
3. Attach Cone to Cube
4. Select Cone and Cube and Create a Level Instance
5. Move that level instance to some x,y,z offset
6. Edit Level Instance and move the Cone.
7. Exit and save the edit
8. Press Play and check the log in Saved/Logs/WorldPartition

Result is that the Cone saves its offsetted location.