PAL: wfopen support longer mode strings and improve compatibility

[obastemur]

Extracted from #3159

_wfopen_s's implementation here limits the mode to 10 chars - so calling _wfopen with "r, ccs=UNICODE" fails since the mode string is longer than 10 chars.

[digitalinfinity]

There is another issue that is noted in #3159 that should also be fixed up here- MapFileOpenModes does not like it if ccs=UNICODE is passed in as the mode string. This should also be fixed as part of fixing this issue. If this is implemented, then ConfigParser::ParseConfig can be updated to not be ifdefed separately for Windows and Linux for the wfopen_s call.