bpo-40260: revert refactor of file_info tuple by barry-scott · Pull Request #19595 · python/cpython

by passing in an fp that is opened in "rb".

This fixes problems seen on Windows where the source code is not
decoded as utf-8 but as the code page default for the user, cp1252
for example.

Add three new tests to test_modulefinder.py to excercise
the decoding of source code.

Always write the test source as bytes to avoid using
locale.getpreferredencoding() as the encoding.

test_coding_default_utf8 - designed to fail if decoded with cp1252
test_coding_explicit_utf8 - designed to fail if decoded with cp1252
test_coding_explicit_cp1252 - designed to fail if decoded with utf-8

Remove the mode in file_info that is usused.

Debian relies on the subclassing ModuleFinder
and load_module call to access info in the file_info
tuple.