Implement Iterator::last for vec::IntoIter

Author: thaliaarchi

Diff for: library/alloc/src/vec/into_iter.rs

@@ -258,6 +258,11 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         self.len()
     }
 
+    #[inline]
+    fn last(mut self) -> Option<T> {
+        self.next_back()
+    }
+
     #[inline]
     fn next_chunk<const N: usize>(&mut self) -> Result<[T; N], core::array::IntoIter<T, N>> {
         let mut raw_ary = [const { MaybeUninit::uninit() }; N];