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.
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v3: create CopyFile2_impl that uses SetLastError error handling
https://gitlab.winehq.org/wine/wine/-/merge_requests/5020