Add zurb foundation widescreen/responsive-embed code to gutenberg video blocks.

assets.php

function foundation_gutenberg_wrappers()
{
    if (defined('WP_DEBUG') && WP_DEBUG) {
        $gutenberg_file = '/js/raw/gutenberg.js?no_cache=' . time();
    } else {
        $gutenberg_file = '/js/raw/gutenberg.js';
    }
    wp_enqueue_script('foundation-gutenberg-extensions', get_template_directory_uri() . $gutenberg_file, array('wp-blocks'));
}
add_action('enqueue_block_editor_assets', 'foundation_gutenberg_wrappers');

gutenberg.js

wp.hooks.addFilter('blocks.getSaveElement', 'foundation/add-foundation-wrappers', addFoundationWrappers)

function addFoundationWrappers(element, blockType, attributes) {
    if ($.inArray(blockType.name, ['core-embed/vimeo', 'core-embed/youtube', 'core-embed/video']) !== -1) {
        element.props.className += ' widescreen responsive-embed';
        return element;
    }
    return element;
}