copy implementation of CopyFileExW into CopyFile2, then implement CopyFileExW in terms of CopyFile2 should fix https://bugs.winehq.org/show_bug.cgi?id=55897, as Python does not use any new functionality nor the callback parameter from CopyFile2. - followed [the Wiki](https://wiki.winehq.org/Developer_Hints#Implementing_new_API_calls) for adding a new API call - run `file.c` tests and they seem to pass I have not written extensive documentation since the original function didn't seem to have any; I can do that if recommended. I originally intended to implement the callback functionality in this MR as well, but realized that would be better as a follow-up. -- v3: create CopyFile2_impl that uses SetLastError error handling https://gitlab.winehq.org/wine/wine/-/merge_requests/5020