Implement serialization of subclasses

[braxtonmckee]

this should work but doesn't, because we don't have a pathway for serializing a subclass of a Class instance where we know the type as the base class. In the below case, we know that a ListOf(C) contains C pointers, and we can stick a 'Subclass' pointer in it. If we serialize the objects individually, the interpreter will dispatch to the Subclass serialize method. But if we serialize the list itself, we end up dispatching to 'C''s serialization routine, which can't handle the child class.

    def test_serialize_subclasses(self):
        class C(Class):
            pass

        class Subclass(C, Final):
            def f(self):
                return 10

        sc = SerializationContext({'Subclass': Subclass, 'C': C})

        listOfClassObjects = ListOf(C)()
        listOfClassObjects.append(Subclass())

        instOfSubclass = sc.deserialize(sc.serialize(listOfClassObjects))[0]

        self.assertIsInstance(instOfSubclass, Subclass)
        self.assertEqual(instOfSubclass.f(), 10)