Constructs a Drupal\Core\Plugin\Discovery\AlterDecorator object.
It uses the DiscoveryInterface object it should decorate.
Drupal\Component\Plugin\Discovery\DiscoveryInterface $decorated: The object implementing DiscoveryInterface that is being decorated.
string $hook: The name of the alter hook that will be used by this discovery instance.
public function __construct(DiscoveryInterface $decorated, $hook) {
$this->decorated = $decorated;
$this->hook = $hook;
}