Also change several error messages to refer to "items" rather than
"methods", since associated items that require resolution during type
checking are not always methods.
closure kind, thereby detecting what happens if there are
mismatches. Simply removing the `:` annotations caused most of these
tests to pass or produce other errors, because the inference would
convert the closure into a more appropriate kind. (The ability to
override the inference by using the expected type is an important
backdoor partly for this reason.)
