P3503R3 — Make type-erased allocator use in promise and packaged_task consistent
LWG
[[LWG2095](https://wg21.link/lwg2095)] points out inconsistencies in the API of `std::promise`; namely that `uses_allocator<promise<R>, A>::value` is specified to be true in 32.10.6 [[futures.promise]](https://wg21.link/futures.promise), yet is missing the appropriate constructor taking an rvalue of promise.