Auto merge of rust-lang#86904 - m-ou-se:prelude-collision-check-trait, r=nikomatsakis

Check FromIterator trait impl in prelude collision check.

Fixes rust-lang#86902.

Author: bors

core/src/iter/traits/collect.rs

@@ -89,6 +89,7 @@
                over elements of type `{A}`",
     label = "value of type `{Self}` cannot be built from `std::iter::Iterator<Item={A}>`"
 )]
+#[rustc_diagnostic_item = "FromIterator"]
 pub trait FromIterator<A>: Sized {
     /// Creates a value from an iterator.
     ///