[varfonts] Query varfonts if id >> 16 == 0x8000

If "instance-number" part of face id is set to 0x8000, return a pattern
for variable font as a whole.  This might have a range for weight, width,
and size.

If no variation is found, NULL is returned.

Not hooked up to FcQueryFaceAll() yet.  For now, can be triggered using
fc-query -i 0x80000000
1 file changed