Return the font name of face FACE, or nil if it is unspecified.
The font name is, by default, for ASCII characters.
If the optional argument FRAME is given, report on face FACE in that frame.
If FRAME is t, report on the defaults for face FACE (for new frames).
The font default for a face is either nil, or a list
of the form (bold), (italic) or (bold italic).
If FRAME is omitted or nil, use the selected frame. And, in this case,
if the optional third argument CHARACTER is given,
return the font name used for CHARACTER.
(fn FACE &optional FRAME CHARACTER)