Passing attributes between theme hooks

gistfile1.txt

function some_theme_preprocess_paragraph(&$variables) {
  $element = &$variables['elements'];
  $paragraph = $variables['paragraph'];

  if ($paragraph->getType() === 'image_gallery') {
    $images = $paragraph->get('field_image_gallery');
    foreach ($images->referencedEntities() as $image) {
      $image->parent_paragraph = $paragraph;
    }
  }
}

 function some_theme_theme_suggestions_media_alter(array &$suggestions, array $variables) {
  $media = $variables['elements']['#media'];
  if ($paragraph = $media->parent_paragraph) {
    $suggestions[] = $variables['theme_hook_original'] . '__' . $media->bundle() . '__' . $paragraph->getType();
  }
}