Allows retrieving the canonical type implementing
Try that has this type
as its residual and allows it to hold an
O as its output.
Result<T, E>: Try<Output = T, Residual = Result<Infallible, E>>,
and in the other direction,
<Result<Infallible, E> as Residual<T>>::TryType = Result<T, E>.
The “return” type of this meta-function.