Shim to fix errors in WP 5.5-alpha+ and WP Mail SMTP

wp-mail-smtp-shim.php

<?php
/**
 * WP Mail SMTP Shim for WP 5.5 plugin bootstrap.
 *
 * @package   WP_Mail_SMTP_Shim
 * @author    Andy Fragen
 * @license   MIT
 *
 * @wordpress-plugin
 * Plugin Name:       WP Mail SMTP Shim for WP 5.5
 * Plugin URI:        https://gist.github.com/afragen/c710026eaa1d1634b637dbf91c726c75
 * Description:       Don't display the deprecated file error for WP Mail SMTP in WP 5.5-alpha+. Deprecated file warning displays as `/wp-includes/class-phpmailer.php` has moved to `/wp-includes/PHPMailer/PHPMailer.php`. Properly load the `class PHPMailer\PHPMailer\SMTP` so `MailCatcher->send()` works.
 * Version:           0.5
 * Author:            Andy Fragen
 * Author URI:        https://thefragens.com/
 * License:           MIT
 * Requires at least: 5.5-alpha
 * Requires PHP:      5.6
 * Gist Plugin URI:   https://gist.github.com/afragen/c710026eaa1d1634b637dbf91c726c75
 */

if ( ! function_exists( 'is_plugin_active' ) ) {
	require_once ABSPATH . 'wp-admin/includes/plugin.php';
}
if ( is_wp_version_compatible( '5.5-alpha' ) && is_plugin_active( 'wp-mail-smtp/wp_mail_smtp.php' ) ) {
	add_filter( 'deprecated_file_trigger_error', '__return_false' );
	add_action(
		'wp_mail_smtp_mailcatcher_smtp_send_before',
		function() {
			if ( ! class_exists( 'PHPMailer\PHPMailer\SMTP' ) ) {
				require_once ABSPATH . WPINC . '/PHPMailer/SMTP.php';
			}
		}
	);
}

Installation instructions: https://gist.github.com/westonruter/6110fbc4bef0c4b8c021a112012f7e9c

Suggest adding require_once( ABSPATH . 'wp-admin/includes/plugin.php' ); to line 21; otherwise, it tends to throw a Fatal error: Uncaught Error: Call to undefined function is_plugin_active() in /var/www/html/wp-content/plugins/wp-mail-smtp-shim.php on line 24 on activation.

Thank you for the shim for use in the meantime!

@pkarjala will do.