Add Windows GDI or DirectWrite fontselect

[rcombs]

After the general internal fontselect changes and CoreText provider are ready, we should look into a Windows provider. @grigorig's fonts branch has at least some amount of work done on a GDI provider (not sure how far along it is?), but we might want to look at DirectWrite instead, since WinXP is out of support anyway.

[feliwir]

Any news on this issue?

[astiob]

Nope. :( Nobody currently has both the time and the motivation to work on this issue.

[ghost]

Also it seems unlikely that grigorig will ever pick this up again.

I'm wondering why we can't just do the same as vsfilter, though. If we can, it should be "relatively" simple.

[astiob]

And doing the same as VSFilter would potentially be better for compatibility, too.

[grigorig]

The fonts branch in grigorig/libass now has a working DirectWrite backend. Please test it!

[feliwir]

It was working fine for me on Win 8.1

[grigorig]

Done.