[FEATURE] Improve BeforeSearchResultIsShownEvent (#3915)

This change allows the developers to provide additional variables to the view of EXT:solr FE plugins.

Relates: #3705

Classes/Controller/SearchController.php

@@ -143,6 +143,7 @@ public function resultsAction(): ResponseInterface
                 'arguments' => $afterSearchEvent->getArguments(),
                 'pagination' => $afterSearchEvent->getPagination(),
                 'currentPage' => $afterSearchEvent->getCurrentPage(),
+                'additionalVariables' => $afterSearchEvent->getAdditionalVariables(),
             ];
 
             $this->view->assignMultiple($values);

Classes/Event/Search/BeforeSearchResultIsShownEvent.php

@@ -33,6 +33,7 @@ final class BeforeSearchResultIsShownEvent
     private array $arguments;
     protected PaginationInterface $pagination;
     private int $currentPage;
+    protected array $additionalVariables = [];
 
     public function __construct(
         SearchResultSet $resultSet,
@@ -84,4 +85,14 @@ public function setPagination(PaginationInterface $pagination): void
     {
         $this->pagination = $pagination;
     }
+
+    public function getAdditionalVariables(): array
+    {
+        return $this->additionalVariables;
+    }
+
+    public function setAdditionalVariables(array $additionalVariables): void
+    {
+        $this->additionalVariables = $additionalVariables;
+    }
 }