This is my order of preference among options so far:

(1) mixed shorthand syntax where explicit parameter types are required and no name implies positional
     - I'd prefer to make no-name-given the *only* way to do positional-only args, i.e. no `/` in the syntax
     - this is not consistent with stub syntax, but it avoids some edge cases we hit otherwise
     - I don't think requiring explicit types is a huge burden, the existing `Callable` type requires it

(2) full stub syntax, with a shorthand syntax for positional-only callables
     - we would have to require explicit Any annotations:
        - otherwise, we get collisions between shorthand syntax and implicit Any
        - for example, is `(a, b) -> int` of type `Callable[[Any, Any], int]` or `Callable[[a, b], int`?

(3) full stub syntax only, with no shorthand
     - it seems like a majority thinks this is burdensome because of existing Callables
     - If we want to be able to revisit shorthand syntax later if we have to require explicit Any
       - otherwise, the ambiguous case described above plus backward compatibility will trap us


If we move forward with options (2) or (3) we'll still have to decide whether to allow _ as the argument name for positional-only args. My preference would be to allow it so that nuisance argnames aren't required, but to require an explicit `/`
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