only in patch2:
unchanged:
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -2305,20 +2305,6 @@ function drupal_merge_js_settings($settings_items) {
   return NestedArray::mergeDeepArray($settings_items, TRUE);
 }
 
 /**
  * #pre_render callback to add the elements needed for JavaScript tags to be rendered.
@@ -3340,7 +3326,7 @@ function drupal_pre_render_links($element) {
     }
     // Merge attachments.
     if (isset($child['#attached'])) {
-      $element['#attached'] = drupal_merge_attached($element['#attached'], $child['#attached']);
+      $element['#attached'] = NestedArray::mergeDeep($element['#attached'], $child['#attached']);
     }
   }
   return $element;
@@ -4078,7 +4064,7 @@ function _drupal_render_process_post_render_cache(array &$elements) {
             if (!isset($modified_elements['#attached'])) {
               $modified_elements['#attached'] = array();
             }
-            $modified_elements['#attached'] = drupal_merge_attached($modified_elements['#attached'], drupal_render_collect_attached($generated_element, TRUE));
+            $modified_elements['#attached'] = NestedArray::mergeDeep($modified_elements['#attached'], drupal_render_collect_attached($generated_element, TRUE));
           }
 
           // Replace the placeholder with the rendered markup of the generated
@@ -4196,7 +4182,7 @@ function drupal_render_collect_attached($elements, $return = FALSE) {
 
   // Collect all #attached for this element.
   if (isset($elements['#attached'])) {
-    $attached = drupal_merge_attached($attached, $elements['#attached']);
+    $attached = NestedArray::mergeDeep($attached, $elements['#attached']);
   }
   if ($children = Element::children($elements)) {
     foreach ($children as $child) {