Deprecated drupal_merge_attached() replaced with BubbleableMetadata::mergeAttachments()

drupal_merge_attached() has been replaced with the static mergeAttachments() method of the BubbleableMetadata class.
Before:

$element['#attached'] = drupal_merge_attached($element['#attached'], $child['#attached']);

After:

$element['#attached'] = BubbleableMetadata::mergeAttachments($element['#attached'], $child['#attached']);