Refactored Node3D rotation modes

* Made the Basis euler orders indexed via enum.
* Node3D has a new rotation_order property to choose Euler rotation order.
* Node3D has also a rotation_mode property to choose between Euler, Quaternion and Basis

Exposing these modes as well as the order makes Godot a lot friendlier for animators, which can choose the best way to interpolate rotations.
The new *Basis* mode makes the (exposed) transform property obsolete, so it was removed (can still be accessed by code of course).

modules/gdscript/tests/scripts/runtime/features/stringify.gd

@@ -17,7 +17,7 @@ func test():
 	print(Plane(1, 2, 3, 4))
 	print(Quaternion(1, 2, 3, 4))
 	print(AABB(Vector3.ZERO, Vector3.ONE))
-	print(Basis(Vector3(0, 0, 0)))
+	print(Basis.from_euler(Vector3(0, 0, 0)))
 	print(Transform3D.IDENTITY)
 
 	print(Color(1, 2, 3, 4))