Create an unordered map having the same value, hasher, key-equality comparator, and max_load_factor as the specified original. Use the allocator returned by 'bsl::allocator_traits<ALLOCATOR>:: select_on_container_copy_construction(original.get_allocator())' to supply memory. If the ALLOCATOR type is bsl::allocator (the default), the currently installed default allocator is used to supply memory.