[clang] [libc++][ranges] Implement ranges::contains_subrange (PR #66963)

[Konstantin Varlamov via cfe-commits]

================
@@ -214,6 +214,19 @@ namespace ranges {
     constexpr ranges::minmax_element_result<borrowed_iterator_t<R>>
       minmax_element(R&& r, Comp comp = {}, Proj proj = {});                                              // since C++20
 
+  template<forward_iterator I1, sentinel_for<I1> S1, forward_iterator I2,
+    sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = identity,
+    class Proj2 = identity>
+    requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
+    constexpr bool ranges::contains_subrange(I1 first1, S1 last1, I2 first2,
----------------
var-const wrote:

Nit: please remove `ranges::` (this code block in synopsis is already within `namespace ranges`).

https://github.com/llvm/llvm-project/pull/66963