Performs autosave with heartbeat.

function heartbeat_autosave( $response, $data ) {
	if ( ! empty( $data['wp_autosave'] ) ) {
		$saved = wp_autosave( $data['wp_autosave'] );

		if ( is_wp_error( $saved ) ) {
			$response['wp_autosave'] = array(
				'success' => false,
				'message' => $saved->get_error_message(),
			);
		} elseif ( empty( $saved ) ) {
			$response['wp_autosave'] = array(
				'success' => false,
				'message' => __( 'Error while saving.' ),
			);
		} else {
			/* translators: Draft saved date format, see https://www.php.net/manual/datetime.format.php */
			$draft_saved_date_format = __( 'g:i:s a' );
			$response['wp_autosave'] = array(
				'success' => true,
				/* translators: %s: Date and time. */
				'message' => sprintf( __( 'Draft saved at %s.' ), date_i18n( $draft_saved_date_format ) ),
			);
		}
	}

	return $response;
}