Make the iter_kv_map lint handle ref/mut annotations.
For the degenerate (`map(|(k, _)| k)`/`map(|(_, v)| v)`) cases a mut annotation is superfluous and a ref annotation won't compile, so no additional handling is required. For cases where the `map` call must be preserved ref/mut annotations should also be presereved so that the map body continues to work as expected.
*Please write a short comment explaining your change (or "none" for internal only changes)*
changelog: [`iter_kv_map`]: handle ref/mut annotations
d5d8ef13d7