Add `Option::unzip_ref`

language design
1

Like Option::unzip, the origin code:

impl<T, U> Option<(T, U)> {
    pub fn unzip(self) -> (Option<T>, Option<U>) {
        match self {
            Some((a, b)) => (Some(a), Some(b)),
            None => (None, None),
        }
    }
}

But different in bound, my idea:

impl<T, U> Option<&(T, U)> {
    pub fn unzip_ref(self) -> (Option<&T>, Option<&U>) {
        match self {
            Some((a, b)) => (Some(a), Some(b)),
            None => (None, None),
        }
    }
}