Make `ignore_pos_arg_names=False` for overrides when using `--extra-checks`

[A5rocks]

Feature

We can check positional argument names for overriding functions.

class A:
    def f(self, x: int) -> None:
        pass
    
class B(A):
    def f(self, _x: int) -> None:  # this *should* error, but doesn't currently
        pass

Pitch

Well, ignoring positional arguments is obviously not type safe. It's annoying, sure, but in my mind that's the class of checks that --extra-checks encompasses (technically correct but annoying).

[hauntsaninja]

I think there's consensus that --extra-checks isn't really the way to go.

Do agree with the feature though, see also #18355

[A5rocks]

Making an opt-in error code also makes sense!