List available fonts matching FONT-SPEC on the current frame.
Optional 2nd argument FRAME specifies the target frame.
Optional 3rd argument NUM, if non-nil, limits the number of returned fonts.
Optional 4th argument PREFER, if non-nil, is a font-spec to
control the order of the returned list. Fonts are sorted by
how close they are to PREFER.
(fn FONT-SPEC &optional FRAME NUM PREFER)