test: Add missing `#![feature(managed_boxes)]`

The tests use managed boxes, but are not perfectly feature-gated because
they use `@` inside macros. (It causes issue after `--pretty expanded`.)
compiletest: Modernize typenames
compiletest: Test `--pretty expanded`

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`.