[libc++][NFC] Run clang-format on libcxx/include again (#95874)

As time went by, a few files have become mis-formatted w.r.t.
clang-format. This was made worse by the fact that formatting was not
being enforced in extensionless headers. This commit simply brings all
of libcxx/include in-line with clang-format again.

We might have to do this from time to time as we update our clang-format
version, but frankly this is really low effort now that we've formatted
everything once.

libcxx/include/__split_buffer

@@ -211,8 +211,8 @@ private:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__split_buffer&, false_type) _NOEXCEPT {}
 
   struct _ConstructTransaction {
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(
-        pointer* __p, size_type __n) _NOEXCEPT
+    _LIBCPP_CONSTEXPR_SINCE_CXX20
+    _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(pointer* __p, size_type __n) _NOEXCEPT
         : __pos_(*__p),
           __end_(*__p + __n),
           __dest_(__p) {}