The Learning MFE had a bug where instructors selecting
'View As: Audit' would find themselves redirected to the
'Enroll Now' page. This was because the Courseware API,
 which powers the MFE, checked courseware access *after*
setting up masquerading--so, instead of checking whether
the instructor had access to view the course, we checked
whether some arbitrary un-enrolled learner would have
access to the course (the answer is generally No).

We fix this by doing what the Legacy courseware index
does: calculate courseware access *before* setting up
masquerading.

TNL-7989