Loads content into the node from its referenced external scene file.
- iOS 9.0+
- macOS 10.11+
- tvOS 9.0+
- watchOS 3.0+
When SceneKit loads the referenced scene file, all children of the scene file’s root node become children of the reference node.
If the node has already been loaded (either automatically, according to the
loading property, or through a previous call to this method), calling this method has no effect.