Fix HarfBuzz support on MS-Windows

Fix HarfBuzz support on MS-Windows

* src/w32uniscribe.c [HAVE_HARFBUZZ]: Include hb-ot.h.
(fn_hb_ot_font_set_funcs, hb_ot_font_set_funcs): Define.
(w32hb_get_font): Call hb_ot_font_set_funcs after creating the
hb_font_t object, to make the code work with versions of
HarfBuzz before 2.0.0.  Problem reported by Stephen Leake
<stephen_leake@stephe-leake.org>.  Solution suggested by
Khaled Hosny <dr.khaled.hosny@gmail.com> in
https://lists.freedesktop.org/archives/harfbuzz/2019-July/007412.html.