ENH: Expanduser in to_file methods GH9066

closes #9066
 
First time contributor, tried to follow all rules as good as possible.
If something is missing please let me know.

As specified in task 9066 tilde in a pathname get resolved into a absolute path.
In case the object is a buffer the buffer will be returned.

I did not add additional tests, since I could not find any module explicitly testing pandas/io/common.py
if that is necessary please let me know how to do that. The current tests are passing on my system and seem to cover the method below.

Best Regards,
I might say something more explicit, e.g., "Paths beginning with ~ will now be expanded to begin with the user's home directory"