LWG3770 const_sentinel_t is missing

Author: burblebee

source/ranges.tex

@@ -66,6 +66,8 @@
     using sentinel_t = decltype(ranges::end(declval<R&>()));                        // freestanding
   template<@\libconcept{range}@ R>
     using const_iterator_t = const_iterator<iterator_t<R>>;                         // freestanding
+  template<@\libconcept{range}@ R>
+    using const_sentinel_t = const_sentinel<sentinel_t<R>>;                         // freestanding
   template<@\libconcept{range}@ R>
     using range_difference_t = iter_difference_t<iterator_t<R>>;                    // freestanding
   template<@\libconcept{sized_range}@ R>