Feature: print type coverage

[Raynos]

To sanity check that your have type coverage on your code you may want to get the checker to pretty-print checked and unchecked code.

Currently the only time code is unchecked is:

• if we early bail & not check a unused function implementation
• if we get an error halfway through an expression and dont check the rest of the expr, aka assignment has lower type coverage if the left hand side is ambigious.
• if there is a bug in the type checker