Creating a Moodle tracker from WP-5349.

In Gmail, email renders an invitation section that shows event information:

While in Outlook, only the attached .ics file is shown:

PHPMailer allows this, but we are not properly attaching the .ics file to execute this: https://github.com/moodle/moodle/blob/15b534da3ede9c3966f994e965ecac7361a21b7f/lib/phpmailer/src/PHPMailer.php#L3014-L3029

This may be resolved by adding the following code to https://github.com/moodle/moodle/blob/15b534da3ede9c3966f994e965ecac7361a21b7f/lib/moodlelib.php#L5577 :

if ($mimetype == 'text/calendar') {

     $icalcontent = file_get_contents($attachment);

     $mail->Ical = $icalcontent;

}

This GitHub issue: https://github.com/PHPMailer/PHPMailer/issues/175
Stackoverflow: https://stackoverflow.com/a/66151376