[jit] fix named tuples as attributes (#37251)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37251

This was broken by recent changes to how we serialize with type tags. We
save a name (like `Dict[str, MyNamedTuple]`) and then relied on the
mobile type parser to resolve that name back into a set of types.

This doesn't work for any NamedTypes as the mobile type parser doesn't
know how to resolve those. The unpickler allows the caller to inject a
type resolver in for this purpose, use that so that when importing in a
non-mobile environment you get the right results.

A second problem also had to be fixed: the SourceImporter type loader
would only load named types directly (e.g. `MyNamedTuple`) and choked if
it was a general type that contained a named tupe (e.g.
`List[MyNamedTuple]`). Fixed that and renamed `loadNamedType` to
`loadType` for clarity.

Test Plan: Imported from OSS

Differential Revision: D21235213

Pulled By: suo

fbshipit-source-id: 16db0f4c5e91a890d67a8687cc8ababa6b94b0f4

test/cpp/jit/test_interface.cpp

@@ -41,7 +41,7 @@ static void import_libs(
       &tensor_table,
       [&](const std::string& name) -> std::shared_ptr<Source> { return src; },
       /*version=*/2);
-  si.loadNamedType(QualifiedName(class_name));
+  si.loadType(QualifiedName(class_name));
 }
 
 void testModuleInterfaceSerialization() {