Remove RES and REF typedefs in favor of spelled out Ref<>

These typedefs don't save much typing compared to the full `Ref<Resource>`
and `Ref<RefCounted>`, yet they sometimes introduce confusion among
new contributors.

scene/resources/sprite_frames.cpp

@@ -195,7 +195,7 @@ void SpriteFrames::_set_animations(const Array &p_animations) {
 		anim.loop = d["loop"];
 		Array frames = d["frames"];
 		for (int j = 0; j < frames.size(); j++) {
-			RES res = frames[j];
+			Ref<Resource> res = frames[j];
 			anim.frames.push_back(res);
 		}