Function position_mark 

fn position_mark(
    face: &hb_font_t<'_>,
    direction: Direction,
    font_funcs: &mut FontFuncsDispatch<'_, '_>,
    glyph: GlyphId,
    pos: &mut GlyphPosition,
    base_extents: &mut GlyphExtents,
    combining_class: u8,
)