R1:5e715c1acac0

Simplify some logic in project controllers

Summary: Ref T10010. Several controlers currently have similar logic for handling tags and slugs, loading projects, and canonicalizing URIs. Clean it up a bit.

Test Plan:
- Visited profile, boards, feed.
- Visited by ID and by tag.
- Visited by non-normal tag (redircted).
- Visited by alternate tag (redirected).
- Visited non-policy project by non-normal tag (redirected into policy error).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010…