[8.x] Fix request dump and dd methods

[seriquynh]

What do I do?

1. I fix the dump docblock because it doesn't only accept array as parameters but also an argument list. These two calls produce the same result.

// it takes an array.
$request->dump(['name', 'age']);

// it takes an argument list.
$request->dump('name', 'age');

2. Because dd method uses ... oparator, $keys in this context will be always an array and the check is unnecessary. dd just need to forward the call to dump and then to end the script.

class Request
{
    public function dd(...$keys)
    {
        $this->dump(...$keys);

        exit(1);
    }
}