Implement the ability to disable classes

* This PR adds the ability to disable classes when building.
* For now it's only possible to do this via command like:
  `scons disable_classes=RayCast2D,Area3D`
* Eventually, a proper UI will be implemented to create a build config file to do this at large scale, as well as detect what is used in the project.

modules/basis_universal/register_types.cpp

@@ -272,7 +272,7 @@ void register_basis_universal_types() {
 	Image::basis_universal_packer = basis_universal_packer;
 #endif
 	Image::basis_universal_unpacker = basis_universal_unpacker;
-	//ClassDB::register_class<TextureBasisU>();
+	//GDREGISTER_CLASS(TextureBasisU);
 }
 
 void unregister_basis_universal_types() {