Account for pathlib chmod setting insecure permissions

The current implementation of B103: set_bad_file_permissions works well for uses of the chmod functions from the os module directly.

It fails to report insecure permissions when the equivalent functions from the pathlib module are being used instead.

As a simple example, consider:

import pathlib

p = pathlib.Path("dummy_file")
p.chmod(0o666)

This should trigger an equivalent warning just as os.chmod("dummy_file", 0o666) currently does.

The code should be generalized to support the pathlib version of the chmod functions as well.

Start by locating the implementation of Bandit's B103: set_bad_file_permissions check and compare its handling of os.chmod with the pathlib.Path.chmod example in this issue. Done means insecure permissions set through pathlib are reported with an equivalent warning to direct os.chmod usage.