WordPress plugin to force the Gutenberg block editor to be wider (full width).

wp-block-editor-full-width.php

<?php
/**
 * Plugin Name: Block Editor Full Width
 * Description: Fix the Gutenberg block editor width to the full window (with a max-width)
 * Author: Patrick Haney
 * Author URI: http://patrickhaney.com
 * Version: 1.0.0
 * Text Domain: block_editor_full_width
 * License: GPL2+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 *
 * @package Block Editor Full Width
 */

function block_editor_full_width() {
    echo '<style>
    .wp-block {
        width: 100% !important;
        max-width: none !important;
    }
    .editor-styles-wrapper .editor-writing-flow {
        /* Set this max-width to whatever you like */
        max-width: 1440px !important;
        margin: 0 auto !important;
    }
    </style>';
}

add_action( 'admin_head', 'block_editor_full_width' );
?>