Add Featured Image URL to Posts REST Response

<?php
if ( ! function_exists( 'scseed_register_featured_image_url_field' ) ) {
    function scseed_register_featured_image_url_field() {
        register_rest_field(
            'post',
            'featured_image_url',
            array(
                'get_callback' => 'scseed_get_featured_image_url',
                'schema'       => array(
                    'description' => __( 'Full URL of the featured image, or null.', 'scseed' ),
                    'type'        => array( 'string', 'null' ),
                    'context'     => array( 'view', 'embed' ),
                    'readonly'    => true,
                ),
            )
        );
    }
    add_action( 'rest_api_init', 'scseed_register_featured_image_url_field' );
}

if ( ! function_exists( 'scseed_get_featured_image_url' ) ) {
    function scseed_get_featured_image_url( $object ) {
        $thumbnail_id = get_post_thumbnail_id( $object['id'] );
        if ( ! $thumbnail_id ) {
            return null;
        }
        $src = wp_get_attachment_image_src( $thumbnail_id, 'full' );
        return $src ? esc_url_raw( $src[0] ) : null;
    }
}