Const adjustments

These changes make const translation use adjustments (autodereference, autoreference, bare-fn-to-closure), like normal code does, replacing some ad-hoc logic that wasn't always right.

As a convenient side-effect, explicit dereference (both of pointers and of newtypes) is also supported in const expressions.

There is also a “bonus fix” for a bug in the pretty-printer exposed by one of the added tests.