Get the difference between old and attributes

[JeremieBergeron]

This idea is very similar with: #745

It would be usefull if we could get all the difference between old and attributes.

Here is an example how we need to do it currently

$changes = $log->changes;
$changes['attributes'] = array_udiff_assoc($changes['attributes'], $changes['old'], function ($a, $b) {
    if ($a === $b) {
        return 0;
    }
    return $a > $b ? 1 : -1;
});

$changes['old'] = collect($changes['old'])->only(array_keys($changes['attributes']))->all();