Decode __file__ using filesystem encoding

If the python packages loaded are in a non-ASCII named directory,
pywikibot on Python 2.x fails with UnicodeDecodeError.

Decode the __file__ values with sys.getfilesystemencoding().

Bug: 69476
Change-Id: I74c8d08b48b4f03ef38ccdbfce8ff3e5886289d5
Merge "Decode __file__ using filesystem encoding"