Clarify a Lint message - Mismatch in type between binder and occurrence

In #17803 (closed), it was noted that the lint error only prints the binder's name, which can lead to confusion when debugging shadowing problems (e.g. when the binder is shadowed, so the binder and occurrence have the same Unique but different Names, due to a bugged plugin).

We now print both the binder and occurrence in this situation.