[HarfBuzz] How to get hb_face_t and hb_font_t without Freetype?

[Eli Zaretskii]

> From: Behdad Esfahbod <behdad at behdad.org>
> Date: Sat, 11 May 2019 11:38:58 -0700
> Cc: Jonathan Kew <jfkthame at gmail.com>, 
> 	"harfbuzz at lists.freedesktop.org" <harfbuzz at lists.freedesktop.org>
> 
> The blob simply hold the font file bytes.  There's even hb_blob_create_from_file.
>  
> Makes sense?

Not sure yet.  What is a "font" for this purpose?  Does it have to be
the full contents of a font file on disk?