The attached patch is a preliminar implementation of a DirectWrite font
driver that allows for color fonts, tested only on Windows 11.

There is much to be refined about quality, performance (caching), OS
version conditionals, etc.

Before doing all that, I need to know that this is the right (or at
least good enough) way to do it.

The DirectWrite font driver mounts on top of a copy of the harfbuzz one,
and then replaces some of the functions, but some of the hb functions
include eassert to check that the driver for a font is harfbuzz. I don't
know how to deal with that.

I suppose that if we skip harfbuzz completely, then we would have to
reimplement a lot of stuff with DirectWrite?

Also uniscribe_open has been modified to change the driver assigned to
the font unconditionally to dwrite.

-- 
Cecilio Pardo