[Typing-sig] Re: PEP-589 TypedDict inheritance rules and typing.Literal / PEP-586

I see, that makes sense. Maybe, in addition to or instead of the immutable=True (or frozen=True) kwarg, we should have TypedMapping or TypedFrozenMap, as part of (or in addition to) the "frozenmap" proposed in PEP-603, "Adding a frozenmap type to collections" (https://www.python.org/dev/peps/pep-0603/).