Visibility fixes for partners that are also applicants (#3893)

Fixes #3892. This solution was a bit unruly (especially ugly after
linting) but it seemed like the logical approach without refactoring the
whole `visibility_for` to be a normal method rather than a class method.
This fix evaluates if the partner/reviewer is the author of the source
submission first before evaluating the their role. The reviewer role was
also lumped in here because even though I know we advise against a
reviewer also being an applicant, it still could happen without
oversight.

I tried to keep the code as clean as I could and reuse QuerySets, but
let me know if y'all see any way I can optimize!