text-freetype2: Split find-font-windows.c

This moves font-finding code that can be shared to find-font.c.
text-freetype2: Do not use fontconfig for mac

Originally, I tested the fontconfig code on mac and it was working
swimmingly.  However, it seems to be related to the fact that I am using
the ports/homebrew version of fontconfig.  Most users do not have that
version, and instead use the system built-in version of fontconfig,
which apparently does not find any mac fonts..  at all.  So, this
reverts the mac code to the older mac code we were using to manually
find and associate fonts with font files on the mac.