3479223: add facet url alias

Closes #3479223

modules/facets/src/EventSubscriber/SearchApiEndpointEventSubscriber.php

@@ -91,6 +91,7 @@ class SearchApiEndpointEventSubscriber implements EventSubscriberInterface {
       $search_response['facets'][] = [
         'label' => $facet->label(),
         'key' => $facet->id(),
+        'alias' => $facet->getUrlAlias(),
         'count' => count($built_facet->getResults()),
         'active_values' => $facet->getActiveItems(),
         'results' => $built_results,