function getCalendarEventURL_(event, cal) {
  const baseCalUrl = 'https://www.google.com/calendar';
  // Joins Calendar Event Id with Calendar Id, then base64 encode to derive the event URL.
  let encodedId = Utilities.base64Encode(event.getId().split('@')[0] + " " + cal.getId()).replace(/\=/g, '');
  encodedId = `/event?eid=${encodedId}`;
  return (baseCalUrl + encodedId);

}
Creates the URL for the Google Calendar event.

@param {object} event The Google Calendar Event instance
@param {object} cal The associated Google Calendar 
@return {string} URL in the form of 'https://www.google.com/calendar/event?eid={event-id}'