Issue #2297681 by cilefen, Wim Leers, cs_shadow | Charles Belov: Added Make...

Issue #2297681 by cilefen, Wim Leers, cs_shadow | Charles Belov: Added Make the "alt" attribute required in EditorImageDialog.

core/modules/editor/src/Form/EditorImageDialog.php

@@ -96,6 +96,7 @@ public function buildForm(array $form, array &$form_state, FilterFormat $filter_
     $form['attributes']['alt'] = array(
       '#title' => $this->t('Alternative text'),
       '#type' => 'textfield',
+      '#required' => TRUE,
       '#default_value' => isset($image_element['alt']) ? $image_element['alt'] : '',
       '#maxlength' => 2048,
     );