Refactor auto-instantiation of Object properties in editor

Auto-instantiation is used by the create dialog, but should also be
used by the editor inspector.

This refactors object properties auto-instantiation into a dedicated
method to be reused throughout editor (and possibly scripting).

editor/editor_data.h

@@ -182,6 +182,8 @@ public:
 	void remove_custom_type(const String &p_type);
 	const Map<String, Vector<CustomType>> &get_custom_types() const { return custom_types; }
 
+	void instantiate_object_properties(Object *p_object);
+
 	int add_edited_scene(int p_at_pos);
 	void move_edited_scene_index(int p_idx, int p_to_idx);
 	void remove_scene(int p_idx);