[Pitch] Last expression as return value

[georgeef]

@ben-cohen

For closures, the last expression will be used to infer the type of the outer closure.

The inferred type of

let x = {
  // some code without return
  return optional?.voidMethod()
}()

depends on the presence or absence of return ('()?' or '()', resp.). What is the type with the last expression rule, if return is removed?