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

[Konstantin Varlamov via cfe-commits]

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@@ -0,0 +1,303 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-steps): -fconstexpr-steps=2000000
+
+// template<input_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+//     requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+//     constexpr bool ranges::contains(I first, S last, const T& value, Proj proj = {});       // since C++23
+
+// template<input_range R, class T, class Proj = identity>
+//     requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+//     constexpr bool ranges::contains(R&& r, const T& value, Proj proj = {});                 // since C++23
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <ranges>
+#include <vector>
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var-const wrote:

Nit: `<vector>` seems unused.

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