Merge linting phases into one megaphase

[szymon-rd]

Unused, shadowing, and other future linting warns should be calculated in one megaphase. Right now, an undiagnosed issue is preventing us from doing that. The issue should be diagnosed and phases put in one megaphase

[som-snytt]

In my version, the problem was the way CheckShadowing was detecting the class type params it wanted. I kludged it a bit.