Renames get_parent_spatial() to get_parent_node3d() and changes its
implementation. Before it was not returning a correct pointer if the
node wasn't added to a SceneTree. Now it uses the same implementation as
CanvasItem, which will be correct even for nodes outside a SceneTree.
Forces the transform to update. Transform changes in physics are not instant for performance reasons. Transforms are accumulated and then set. Use this if you need an up-to-date transform when doing physics operations.