Add harfbuzz FFI

[ezdiy]

Full binding, so as to avoid type dep annoyances in the future.
Primarily for mupdf font queries, but perhaps also more generally,
cf koreader/koreader#6763

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This change is 

[Frenzie]

Fine by me, we probably don't really need the whole shebang from the get-go though?

[ezdiy]

@Frenzie Almost-automated fire and forget thing via bunch of :%s macros.

@NiLuJe was wondering the same after I spammed inkview the same way. Indeed there's no need for full cdecl, but figuring what to cherry pick while you're prototyping splits loyalties, as you need to regenerate the header repeatedly and deal with the cascades of type dependencies. Albeit I a admit it's a little bit bloaty (5kb vs 50k lua file), perf wise the impact is not measurable.

[NiLuJe]

It's fine by me if there's no perf impact ;).

I tend to like hand-tailored cdecls because it serves as a bit of documentation in the sense of: "hey, here are the things I'll probably be using", but it's more of a personal choice than anything, really ;).

[Frenzie]

That's why I like it too, I think it makes it easier to grok what's going on. Besides that it's irrelevant.