Add return types to tests and final|internal|private methods

Author: nicolas-grekas

Tests/AbstractCrawlerTest.php

@@ -1241,6 +1241,9 @@ protected function createNodeList()
 
 class ClassThatInheritCrawler extends Crawler
 {
+    /**
+     * @return static
+     */
     public function children()
     {
         parent::children();