Port rust-lang/rust changes for Iterator, Extend

- #62316: When possible without changing semantics, implement
  Iterator::last in terms of DoubleEndedIterator::next_back for types in
  liballoc and libcore
- #59740: Use for_each to extend collections

Author: clint-white

src/binary_heap.rs

@@ -1412,6 +1412,11 @@ impl<'a, T> Iterator for Iter<'a, T> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
+
+    #[inline]
+    fn last(self) -> Option<&'a T> {
+        self.iter.last()
+    }
 }
 
 // #[stable(feature = "rust1", since = "1.0.0")]
@@ -1652,9 +1657,7 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
 
         self.reserve(lower);
 
-        for elem in iterator {
-            self.push(elem);
-        }
+        iterator.for_each(move |elem| self.push(elem));
     }
 }