Get rid of fake TypeInfo's for TypedDicts

We currently create fake TypeInfos to store TypedDicts. This used to cause various issues, in particular, currently the type of a TypedDict "class object" in runtime context is () -> SomeTypedDict, where the return type is an instance of the fake TypeInfo.

We can probably fix latter by just constructing a reasonable type, but a more global solution would be to get rid of the fake TypeInfo entirely. It is not needed for anything and just complicates things. We will need to put some symbol node in the symbol table, so we would need a new SymbolNode subclass (or reuse TypeAlias, so a TypedDict definition A = TypedDict('A' {'x': int, 'y': int}) will be very similar to A = Dict[str, int]).

Empieza rastreando dónde las definiciones de TypedDict crean TypeInfos ficticios y cómo se almacenan sus símbolos en la tabla de símbolos. Evalúa una nueva subclase de SymbolNode o una representación de TypeAlias y, después, verifica que los TypedDicts ya no requieran TypeInfos ficticios y que su tipo de objeto de clase en el contexto de ejecución sea razonable.