I had specially exposed the API as I didn't know how to embed harfbuzz
easily elsewhere but now with harfbuzz.cc it has become very easy
and I don't like to see its use anywhere as it has a bad naming and
its Kashida adding is bogus and only useful to check where it should
be added, not visually useful however.
It makes a hb_face_t from IDWriteFontFace, useful when using
DirectWrite facilities for font selection, loading and rendering
but using harfbuzz for shaping.
Ebrahim Byagowi
Behdad Esfahbod