[libcxx][ranges] Add `ranges::iter_swap`.

Differential Revision: https://reviews.llvm.org/D102809

NOKEYCHECK=True
GitOrigin-RevId: 40d6d2c49dd16641a6fd40916e1cc9a58513ed15
diff --git a/include/iterator b/include/iterator
index 929cc16..0b5c4ee 100644
--- a/include/iterator
+++ b/include/iterator
@@ -562,6 +562,7 @@
 #include <__iterator/default_sentinel.h>
 #include <__iterator/incrementable_traits.h>
 #include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
 #include <__iterator/prev.h>