mypy

58514a9c - stubtest: error if module level dunder is missing, housekeeping (#12217)

stubtest: error if module level dunder is missing, housekeeping (#12217) Basically a follow up to #12203 New errors in typeshed from this: ``` _decimal.__libmpdec_version__ is not present in stub _heapq.__about__ is not present in stub builtins.__build_class__ is not present in stub cgitb.__UNDEF__ is not present in stub decimal.__libmpdec_version__ is not present in stub sys.__unraisablehook__ is not present in stub ``` Some general housekeeping, moving things around, renaming things, adding some comments.