Add `new_child` method to add child nodes from scenes
Closes godotengine/godot-proposals#260. Helps #6521, also see https://github.com/godotengine/godot/issues/6521#issuecomment-559032334.
Ducks.
Closes godotengine/godot-proposals#260. Helps #6521, also see https://github.com/godotengine/godot/issues/6521#issuecomment-559032334.
Ducks.