[WP] Overriding default Gutenberg gallery block

To override the default Gutenberg gallery with the RoyalSlider on the frontend:

1. Create "gallery" type of slider.
   
2. Add the code below to your theme functions.php.
   
3. Replace royalslider="1" with the ID of the slider that you created.
   
4. Go to RoyalSlider Settings page and check an option to include JS/CSS files on all pages (as auto-detection of the shortcode will not work).

function rs_override_gallery_block($block_content, $block) {
        if ( $block['blockName'] !== "core/gallery" ) {
            return $block_content;
        }
        if ( !array_key_exists( 'attrs', $block ) || !is_array( $block['attrs'] ) || !array_key_exists( 'ids', $block['attrs'] ) || !is_array( $block['attrs']['ids'] ) ) {
            return $block_content;
        }
        return do_shortcode('[gallery royalslider="1" ids="' . implode(',', $block['attrs']['ids']) . '"]');
}
add_filter('render_block', 'rs_override_gallery_block', 11, 2);