P2165R4 added a pair-like constructor to std::pair but didn't add a corresponding uses_allocator_construction_args overload. It was in P2165R3 but incorrectly removed during the small group review.

Without LWG 3525, not having the overload would have caused emplacing a pair-like into a pmr::vector<pair> to be outright ill-formed.

With that issue's resolution, in cases where the constructor is not explicit we would create a temporary pair and then do uses-allocator construction using its pieces, and it still won't work when the constructor is explicit.

We should just do this properly.