Use of TypedDict in ListFilter.choices makes it hard to subclass

[strokirk]

Hello!

In #2004, the return type of ListFilter.choices was changed to use a private TypedDict. However, since TypedDict is not a subclass of dict, this introduces extra friction when implementing a new SimpleListFilter. For example, this example will fail since dict cannot be used in place of _ListFilterChoices:

class ExampleFilter(SimpleListFilter):
    ...

    def choices(self, changelist: ChangeList) -> Iterator[dict]:
        for lookup, title in self.lookup_choices:
            yield {
                "selected": self.value() == lookup,
                "query_string": changelist.get_query_string(
                    {self.parameter_name: lookup}
                ),
                "display": title.upper(),
            }

As a workaround, the application developer can of course either duplicate _ListFilterChoices locally, or use Any, but either isn't very ergonomic to my eyes.