Prettier + more-discoverable source for non-exposed modules

In the same way that I can currently click to see the source of any exposed module on hackage, it would be very nice to be able to see the test suite for a package.

(Maybe this is a larger issue? It would be nice to be able to see the source of e.g. executables and internal modules also. The test suite is definitely the most pressing to me, though.)

Start by tracing how Hackage currently exposes source links for package modules. Compare that path with how test suites, executables, and internal modules are represented, prioritizing test-suite browsing; done means a package's test suite can be discovered and viewed like an exposed module.

Written by the indexing model from the issue text.