Add suggestion for iterators in iterators

Author: kper

core/src/iter/traits/iterator.rs

@@ -93,6 +93,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
     message = "`{Self}` is not an iterator"
 )]
 #[doc(spotlight)]
+#[rustc_diagnostic_item = "Iterator"]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 pub trait Iterator {
     /// The type of the elements being iterated over.