Support creating Gio.File.new_for_path from pathlib.Path
On gnome-nightly:
>>> import gi
>>> from pathlib import Path
>>> from gi.repository import Gio
>>> Gio.File.new_for_path(Path("foo"))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Must be bytes, not PosixPath
>>>