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.

servers/rendering/renderer_rd/storage_rd/material_storage.cpp

@@ -2091,7 +2091,7 @@ void MaterialStorage::global_variables_load_settings(bool p_load_textures) {
 				}
 
 				String path = value;
-				RES resource = ResourceLoader::load(path);
+				Ref<Resource> resource = ResourceLoader::load(path);
 				ERR_CONTINUE(resource.is_null());
 				value = resource;
 			}