[clang-tools-extra] [clang] [llvm] [libcxx] [libc++][span] P2821R5: span.at() (PR #74994)

[Nikolas Klauser via cfe-commits]

================
@@ -343,6 +347,15 @@ public:
         return __data_[__idx];
     }
 
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __idx) const {
+      if (__idx >= size()) {
+        __throw_out_of_range();
+      }
+      return *(data() + __idx);
----------------
philnik777 wrote:

```suggestion
      if (__idx >= size())
        __throw_out_of_range();
      return data()[__idx];
```
Maybe also rename `__idx` to `__index` for better readability. Same below

https://github.com/llvm/llvm-project/pull/74994