glob-win: support Unicode

glob-win.c wasn't big, so it was easier to rewrite it. The new version
supports Unicode, handles directories properly, sorts the output and
puts all its allocations in the same talloc context to simplify the
implementation of globfree.

Notably, the old glob had error checking code, but didn't do anything
with the errors since the error reporting code was commented out. The
new glob doesn't copy this behaviour. It just treats errors as if there
were no more matching files, which shouldn't matter for mpv, since it
ignores glob errors too.

To match the other Windows I/O helper functions, the definition is moved
to osdep/io.h.
parse_commandline: glob filenames on Windows

The Windows port uses CommandLineToArgvW, which doesn't expand wildcards
in command line arguments. Use glob to expand them instead, but only for
non-option arguments.