Raise an error when a function isn't well typed and can't be inferred from a callback to type annotation

[kevinbarabash]

The following are acceptable:

let add: (a: number, b: number) => number = (a, b) => a + b;
let foo = (reducer: (action: Action, state: State) => State)): State => {
  return ...
}
foo((action, state) => { ... })

The following are not acceptable:

let fst = (a, b) => a;
let snd = (a, b) => b;