Fix type printer test

Forgot to change the test string for commit
b5bc36391693baa1b1953f7860d2d0b0821e9830
Export `type-mismatch` and use pretty-printing

Previously, the internal `expected-but-got` handled the
pretty-printing but it makes more sense to do it in
`type-mismatch` since it's useful for other modules.
Update TR mutation error message to new format
Make TR tests pass with contracts on again