* include/std/memory (uses_allocator_construction_args): New set of
overloaded functions.
(make_obj_using_allocator, uninitialized_construct_using_allocator):
New functions.
* include/std/memory_resource (polymorphic_allocator::construct)
[__cplusplus > 201703l]: Replace all overloads with a single function
using uses_allocator_construction_args.
* testsuite/20_util/polymorphic_allocator/construct_c++2a.cc: New
test.
* testsuite/20_util/uses_allocator/make_obj.cc: New test.
From-SVN: r269311
