The initial port into JDK 9 used harfbuzz 1.0.6
Later, in 1.2.3 harfbuzz deprecated hb_font_funcs_set_glyph_func ()
and replaced it with
hb_font_funcs_set_nominal_glyph_func() - to handle base glyphs hb_font_funcs_set_variation_glyph_func() - to handle variation sequences
At least that is my presumption of the intent.

We should, as time allows, migrate to the newer API.