[php] Implement native iterator on arrays

[benmerckx]

This one implements php's Iterator on arrays using the internal array position. It eases interfacing with generated haxe code from the php side. (Eg. allows us to foreach ($anyHaxeArray as $key => $item)).

[RealyUniqueName]

Haxe's Array should implement Php's IteratorAggregate instead of Iterator, then this would be possible:

foreach($haxeArray as $key => $value) {
    foreach($haxeArray as $key2 => $value2) {
    }
}