Rollup merge of #140625 - paolobarbolini:vec-extract-if-alt-is-retain_mut, r=Mark-Simulacrum

Suggest `retain_mut` over `retain` as `Vec::extract_if` alternative

The docs for `Vec::extract_if` suggest using `Vec::retain` if the user doesn't need the removed item. Given that `extract_if` gives a mutable reference to the evaluated element, `retain_mut` is the most appropriate alternative, not `retain`.

Author: tgross35

library/alloc/src/vec/mod.rs

@@ -3659,9 +3659,9 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
     /// or the iteration short-circuits, then the remaining elements will be retained.
-    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
+    /// Use [`retain_mut`] with a negated predicate if you do not need the returned iterator.
     ///
-    /// [`retain`]: Vec::retain
+    /// [`retain_mut`]: Vec::retain_mut
     ///
     /// Using this method is equivalent to the following code:
     ///