Avoid removing Course access when unenrolling student in membership

[brianhogg]

Description

Check the current auto-enroll courses list for other memberships a student is a part of before unenrolling the student from a course.

Note that when a student is unenrolled from a membership, we're only maybe unenrolling them from courses that they were not already enrolled in when they were enrolled in the membership. For example:

• Student not enrolled in any courses
• Student enrolled in membership A which auto-enrolls in course A and B
• Student enrolled in membership B which auto-enrolls in course B

Because the student was already enrolled in course A and B, there is no new enrollment record created for course B, so they'll never be unenrolled automatically in course B when they are unenrolled from membership B. This is existing behaviour that would either need a change for what courses we look to remove them from (ie. the current auto-enroll courses list, which may have changed since the student was enrolled in the first place) or creating multiple enrollment triggers that can be checked upon unenrollment in the membership.

• Edit: Now creates a new enrollment record for the membership that is keeping them in the course

Fixes #1861

How has this been tested?

Manually and via PHPUnit test

Checklist:

• This PR requires and contains at least one changelog file.
• My code has been tested.
• My code passes all existing automated tests.
• My code follows the LifterLMS Coding & Documentation Standards.