Blender Git Loki

Fix T86379: When using "Append" not handling properly RigidBody constraints

This was simply never handled apparently.

Also fixes a regression from recent append refactor that prevented RB
objects to to properly handled too (since we instantiate loose objects
in append step now, we need to handle RigidBody ones after that
instantiation stage, otherwise nothing will happen since loose objects
won't be in any scene).