Using #item_attributes with image_formatter and responsive_image_formatter is deprecated

A few theme hooks used an item_attributes property instead of using the standard attributes.

To avoid special case handling, those theme hooks now use attributes.

Before:

      $elements[$delta] = [
        '#theme' => 'image_formatter',
        '#item_attributes' => [
          'loading' => $this->getSetting('image_loading')['attribute'],
        ],
        ...
      ];

      $elements[$delta] = [
        '#theme' => 'responsive_image_formatter',
        '#item_attributes' => $item_attributes,
        ...
      ];

After:

      $elements[$delta] = [
        '#theme' => 'image_formatter',
        '#attributes' => [
          'loading' => $this->getSetting('image_loading')['attribute'],
        ],
        ...
      ];

      $elements[$delta] = [
        '#theme' => 'responsive_image_formatter',
        '#attributes' => $item_attributes,  // Variable $item_attributes not renamed for easier comparison.
        ...
      ];