[libc++][ranges] P3060R3: Add std::views::indices(n)

Implements: P3060R3

# References
- cplusplus/draft#7966
- cplusplus/draft#8006
- https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3060r2.html

Author: H-G-Hristov

libcxx/include/CMakeLists.txt

@@ -714,6 +714,7 @@ set(files
   __ranges/enable_view.h
   __ranges/filter_view.h
   __ranges/from_range.h
+  __ranges/indices_view.h
   __ranges/iota_view.h
   __ranges/istream_view.h
   __ranges/join_view.h

libcxx/include/__ranges/indices_view.h

@@ -0,0 +1,49 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___RANGES_INDECES_VIEW_H
+#define _LIBCPP___RANGES_INDECES_VIEW_H
+
+#include <__assert>
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__ranges/iota_view.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+namespace ranges {
+
+namespace views {
+
+inline constexpr auto indices = [](__integer_like auto __size) {
+  return ranges::views::iota(decletype(__size), __size);
+};
+
+inline namespace __cpo {
+
+} // namespace __cpo
+} // namespace views
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 26
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_INDECES_VIEW_H

libcxx/include/module.modulemap.in

@@ -1887,6 +1887,7 @@ module std [system] {
       export std.functional.bind_back
     }
     module from_range                     { header "__ranges/from_range.h" }
+    module indices_view                   { header "__ranges/indices_view.h" }
     module iota_view                      { header "__ranges/iota_view.h" }
     module istream_view                   { header "__ranges/istream_view.h" }
     module join_view                      { header "__ranges/join_view.h" }

libcxx/include/ranges

@@ -453,6 +453,10 @@ namespace std {
 #    include <__ranges/zip_view.h>
 #  endif
 
+#  if _LIBCPP_STD_VER >= 26
+#    include <__ranges/indeces_view.h>
+#  endif
+
 #  include <version>
 
 // standard-mandated includes