R1:16d8e806a0bc

Simplify ProjectQuery handling of viewer membership

Summary:
Ref T10010. Currently, we do an unusual JOIN to make testing for viewer membership in projects a little cheaper.

This won't work as-is once we have subprojects, so standardize, simplify, and cover it with more tests for now. (I may be able to get a similar optimization later, but want a correct implementation first.)

Test Plan:
This change should create no behavioral differences.

- Added tests.
- Ran tests.
- Viewed projects.

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