Make it so more type-system types can be printed in a shortened version (like `Predicate`s).
Centralize printing the information about the "full type name path".
Make the "long type path" for the file where long types are written part of `Diag`, so that it becomes easier to keep track of it, and ensure it will always will be printed out last in the diagnostic by making its addition to the output implicit.
Tweak the shortening of types in "expected/found" labels.
Remove dead file `note.rs`.
Passing an explicit boolean value (`on`, `off` etc.) appears to work, but
actually puts the compiler into an unintended state where unstable _options_
are still forbidden, but unstable values of _some_ stable options are allowed.
