[PP-1] Test cases for extra field drag&drop issue

To prevent code-duplication, perhaps we could do something like

diff --git a/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php b/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
+  /**
+   * Tests drag&drop of an extra field from hidden to content area.
+   *
+   * @param string $table_drag_selector
+   *   The table drag selector of the extra field.
+   */
+  public function testHiddenExtraFields(string $table_drag_selector = ''): void {
+    if ($table_drag_selector === '') {
+      $table_drag_selector = '.handle';
+    }
+
+   [testy-test]
+  }

diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Theme/ClaroEntityDisplayTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Theme/ClaroEntityDisplayTest.php

+  /**
+   * {@inheritdoc}
+   */
+  public function testHiddenExtraFields(string $table_drag_selector = ''): void {
+    parent::testHiddenExtraFields('.js-tabledrag-handle');
+  }
+