After testing `--pretty normal`, it tries to run `--pretty expanded` and
typecheck output.
Here we don't check convergence since it really diverges: for every
iteration, some extra lines (e.g.`extern crate std`) are inserted.
Some tests are `ignore-pretty`-ed since they cause various issues
with `--pretty expanded`.
When tests fail, their stdout and stderr is printed as part of the summary, but
this helps suppress failure messages from #[should_fail] tests and generally
clean up the output of the test runner.
Tests now have the same name as the test that they're running (to allow for
easier diagnosing of failure sources), and the main task is now specially named
<main> instead of <unnamed>.
Closes#10195Closes#10073