[libc++] Implement ranges::iota (#68494)

# Overview

As a disclaimer, this is my first PR to LLVM and while I've tried to
ensure I've followed the LLVM and libc++ contributing guidelines,
there's probably a good chance I missed something. If I have, just let
me know and I'll try to correct it as soon as I can.

This PR implements `std::ranges::iota` and
`std::ranges::out_value_result` outlined in
[P2440r1](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2440r1.html).

As outlined in the paper above, I've:
- Implemented `out_value_result` and added to `<algorithm>`
- Added `out_value_result`, `iota_result`, and two overloads of `iota`
to `std::ranges` in `<numeric>`
- Updated the version macro `__cpp_lib_ranges_iota` in `<version>`

I've also added tests for `ranges::iota` and `ranges::out_value_result`.
Lastly, I added those structs to the appropriate module files.

Partially implements #105184

EDIT: Forgot to mention in the original post, thanks to @hawkinsw for
taking a look at a preliminary version of this PR!

# TODOs
- [x] Updating the range [status
doc](https://github.com/jamesETsmith/llvm-project/blob/main/libcxx/docs/Status/RangesMajorFeatures.csv)
- [x] Ensure all comments from https://reviews.llvm.org/D121436 are
addressed here
- [X] EDIT (I'll do this in a separate PR). ~~I'm open to implementing
the rest of P2440r1 (`ranges::shift_left` and `ranges::shift_right`) if
that's ok, I just wanted to get feedback on `ranges::iota` first~~
- [x] I've been having trouble building the modules locally and want to
make sure that's working properly

Closes: #134060

1 files changed, 4 insertions, 0 deletions

diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 6ba903a..bf67d33 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -45,6 +45,9 @@ namespace ranges {
   template <class I, class T>
     struct in_value_result;              // since C++23
 
+  template <class O, class T>
+    struct out_value_result;             // since C++23
+
   template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
     indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>                                   // since C++20
   constexpr I min_element(I first, S last, Comp comp = {}, Proj proj = {});
@@ -1936,6 +1939,7 @@ template <class BidirectionalIterator, class Compare>
 #    include <__algorithm/in_out_result.h>
 #    include <__algorithm/lexicographical_compare_three_way.h>
 #    include <__algorithm/min_max_result.h>
+#    include <__algorithm/out_value_result.h>
 #    include <__algorithm/ranges_adjacent_find.h>
 #    include <__algorithm/ranges_all_of.h>
 #    include <__algorithm/ranges_any_of.h>