Implement move_sentinel and C++20 move_iterator.

Differential Revision: https://reviews.llvm.org/D117656

NOKEYCHECK=True
GitOrigin-RevId: 2fb026ee4d1a612f55d3f179b42b223d00ec8eda
diff --git a/include/module.modulemap b/include/module.modulemap
index 6cfa65c..044809f 100644
--- a/include/module.modulemap
+++ b/include/module.modulemap
@@ -661,6 +661,7 @@
       module iterator_traits       { private header "__iterator/iterator_traits.h" }
       module mergeable             { private header "__iterator/mergeable.h" }
       module move_iterator         { private header "__iterator/move_iterator.h" }
+      module move_sentinel         { private header "__iterator/move_sentinel.h" }
       module next                  { private header "__iterator/next.h" }
       module ostream_iterator      { private header "__iterator/ostream_iterator.h" }
       module ostreambuf_iterator   {