ETSConfig.user_data without PyWin32

See https://github.com/enthought/canopy/issues/4609

Currently `ETSConfig._initialize_user_data` on Windows will fallback to a manually constructed path if PyWin32 is not installed. This path is not valid if the user's `[My ]Documents` folder has been moved, and will likely not work on some versions of Windows even when it hasn't been moved.

I propose that a solution based on `ctypes` be used instead of PyWin32 since it is included with Python and has been for quite some time. We have an example of using `ctypes` to get to `SHGetFolderPath` here: https://github.com/enthought/canopy/blob/571649e7b27974b2e3c59eb5a6144adf15171714/canopy/_win32/shell32.py