Implicit all combinator for coroutines

[kelunik]

I think it makes sense to support yielding arrays as implicit all combinator, especially with the changes in PHP 7.1 allowing [] for restructuring.

<?php

function coroutine() {
    [$a, $b, $c] = yield [
        asyncOperation1(),
        asyncOperation2(),
        asyncOperation3(),
    ];
};

[bwoebi]

Ad.: Whenever we implement await in PHP, I'd like to see await accepting these arrays too.