[HarfBuzz] Support for Stylistic Sets

[Eli Zaretskii]

> Date: Sun, 15 Sep 2019 12:37:25 +0100
> From: Richard Wordingham <richard.wordingham at ntlworld.com>
> 
> > > > Does HarfBuzz guess the language?  
> > >
> > > Yes.
> 
> It seems to use the current locale.  That will usually be wrong for
> cuneiform, and generally be wrong for multilingual text.

But Emacs currently doesn't know better anyway.  When it does, we will
pass that information to HarfBuzz, but for now I see no reason to
replace HarfBuzz's guess based on the locale by Emacs's guess based on
that same locale.