Fix pretty HIR for anon consts in diagnostics
This removes the `NoAnn` printer which skips over nested bodies altogether, which is confusing, and requires users of `{ty|qpath|pat}_to_string` to pass in `&tcx` which now impleemnts `hir_pretty::PpAnn`.
There's one case where this "regresses" by actually printing out the body of the anon const -- we could suppress that, but I don't expect people to actually get anon consts like that unless they're fuzzing, tbh.
r? estebank
ac174ae8d2