[libc++] P2944R3: Constrained comparisions - tuple

Implements P2944R3 partially, which adds constrained comparisons `std::tuple`.
The missing overloads introduced in P2165R4 are not implemented.

Relates to #136765

# References

[tuple.rel](https://eel.is/c++draft/tuple.rel)

Author: H-G-Hristov

libcxx/include/tuple

@@ -1155,15 +1155,13 @@ struct __tuple_equal<0> {
 
 template <class... _Tp, class... _Up>
 #    if _LIBCPP_STD_VER >= 26
-  requires(requires(const _Tp& __t, const _Up& __u) {
-            { __t == __u } -> __boolean_testable;
-          } && ...) && (sizeof...(_Tp) == sizeof...(_Up))
+  requires(__all<requires(const _Tp& __t, const _Up& __u) {
+             { __t == __u } -> __boolean_testable;
+           }...>::value && (sizeof...(_Tp) == sizeof...(_Up)))
 #    endif
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y) {
-#    if _LIBCPP_STD_VER < 26
   static_assert(sizeof...(_Tp) == sizeof...(_Up), "Can't compare tuples of different sizes");
-#    endif
   return __tuple_equal<sizeof...(_Tp)>()(__x, __y);
 }