Refactored the facet block label code

Issue #3450329: Refactored the code to fetch the correct block label.

src/Plugin/Block/FacetsBlock.php

@@ -256,15 +256,9 @@ class FacetsBlock extends BlockBase implements ContainerFactoryPluginInterface {
           $build['#attributes'] = [];
         }
 
-        if (
-          isset($build['0']['#facet']) &&
-          $build['0']['#facet'] instanceof FacetInterface
-        ) {
-          $title = $build['0']['#facet']->getName();
-        }
-        else {
-          $title = $block_plugin->label();
-        }
+        /** @var \Drupal\facets\Entity\Facet $facet */
+        $facet = $this->entityTypeManager->getStorage('facets_facet')->load($block_plugin->getDerivativeId());
+        $title = ($facet instanceof FacetInterface) ? $facet->getName() : $block_plugin->label();
 
         // Inject unique class per facet.
         $build['#attributes']['class'][] = strtr($plugin_id, '_:', '--');