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]).

Start by tracing where TypedDict definitions create fake TypeInfos and how their symbols are stored in the symbol table. Evaluate a new SymbolNode subclass or TypeAlias representation, then verify that TypedDicts no longer require fake TypeInfos and that their runtime-context class-object type is reasonable.