[13.x] Add concurrent to Arr

[shaedrich]

Current

Looping over multiple arrays in parallel can be cumbersome or even imperformant when done poorly.

$foo = [1, 2];
$bar = [3, 4];

foreach ($foo as $fooKey => $fooValue) {
	foreach ($bar as $barKey => $barValue) {
		//
	}
}

// or

foreach ($foo as $fooKey => $fooValue) {
	$barValue = $bar[$fooKey];
	//
}

Proposed

$foo = [1, 2];
$bar = [3, 4];
$baz = Arr::concurrent($foo, $bar);

foreach ($baz as $key => [$fooValue, $barValue]) {
	//
}

This is especially helpful when having more than just two arrays.

[shaedrich]

Failing tests seem to be unrelated