Add extend

[CR7273868]

pub fn extend(&self, iter: impl IntoIterator<Item = T>) {
    self.raw.extend(iter)
}

GOES into impl VEC

    pub fn extend(&self, iter: impl IntoIterator<Item = T>) {
        for value in iter {
            self.push(value);
        }
    }

I will do a push request later, once I tested but for now I scrambled this togethger.