Docs(lib/extract_if): Unify paragraph about elements mutation

Take the one from `BTreeMap` that seems the best-worded and most
precise among the available variations.

Signed-off-by: Paul Mabileau <paul.mabileau@harfanglab.fr>

Author: PaulDance

library/alloc/src/collections/linked_list.rs

@@ -1132,8 +1132,8 @@ impl<T, A: Allocator> LinkedList<T, A> {
     /// or the iteration short-circuits, then the remaining elements will be retained.
     /// Use `extract_if().for_each(drop)` if you do not need the returned iterator.
     ///
-    /// Note that `extract_if` lets you mutate every element in the filter closure, regardless of
-    /// whether you choose to keep or remove it.
+    /// The iterator also lets you mutate the value of each element in the
+    /// closure, regardless of whether you choose to keep or remove it.
     ///
     /// # Examples
     ///

library/alloc/src/vec/mod.rs

@@ -3692,8 +3692,8 @@ impl<T, A: Allocator> Vec<T, A> {
     /// But `extract_if` is easier to use. `extract_if` is also more efficient,
     /// because it can backshift the elements of the array in bulk.
     ///
-    /// Note that `extract_if` also lets you mutate the elements passed to the filter closure,
-    /// regardless of whether you choose to keep or remove them.
+    /// The iterator also lets you mutate the value of each element in the
+    /// closure, regardless of whether you choose to keep or remove it.
     ///
     /// # Panics
     ///

library/std/src/collections/hash/map.rs

@@ -654,8 +654,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// yielded. If the closure returns `false`, or panics, the element remains
     /// in the map and will not be yielded.
     ///
-    /// Note that `extract_if` lets you mutate every value in the filter closure, regardless of
-    /// whether you choose to keep or remove it.
+    /// The iterator also lets you mutate the value of each element in the
+    /// closure, regardless of whether you choose to keep or remove it.
     ///
     /// 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.