Registrants on waitlist not added if event "total number of spaces" increased

Problem/Motivation

When increasing the Total Number of Spaces for an Event Series, this does not trigger registrants on the waitlist to be promoted to full registrants.

In other words, when total number of spaces is set to 1 and there are 2 registrants -- one fully registered and one on waitlist -- increasing the total number of spaces to 2 does not cause the waitlisted registrant to become a fully registered one. They remain on the waitlist.

Steps to reproduce

From brand new install:

install with minimal profile

enable recurring_events and recurring_events_registration
- enables field_inheritance, datetime_range, options as dependencies
enable admin_toolbar (just to make nav easier)
- enables breakpoint and toolbar as dependencies

/events/add/default to add new event
- Custom/Single Event with date in future
- Enable Registration
- Individual Event Registration
- Open Registration
- Total Number of Spaces Available = 1
- Enable Waiting List

/events/1/registrations/add to register at least 2 registrants
- one will be put on waiting list
- check /events/1/registrations to verify 2 registrants with one on the waiting list

/events/series/1/edit to edit the Event Series
- change the Total Number of Spaces Available to 2 and save the Event Series
- see a message like "Successfully updated 1 instance statuses. Skipped 0 instances due to status or workflow mismatch with series."

- check /events/1/registrations to see that with new capacity of 2, one of the registrants is still on the waitlist

Proposed resolution

If total number of spaces is increased, for each Event Instance, the "promoteFromWaitlist" method should be called for the number of new spots that have become available. Or this should at least be an option presented to users when changing the total number of spaces -- "Do you want to fill the new spaces from the waitlist?"