Adds an outbound processor object to the $outboundProcessors property.
\Drupal\Core\PathProcessor\OutboundPathProcessorInterface $processor: The processor object to add.
int $priority: The priority of the processor being added.
public function addOutbound(OutboundPathProcessorInterface $processor, $priority = 0) {
$this->outboundProcessors[$priority][] = $processor;
$this->sortedOutbound = array();
}