pub fn gsub_apply_khmer( dotted_circle_index: u16, gsub_cache: &LayoutCache<GSUB>, gsub_table: &LayoutTable<GSUB>, gdef_table: Option<&GDEFTable>, script_tag: u32, lang_tag: Option<u32>, glyphs: &mut Vec<RawGlyph<()>>) -> Result<(), ShapingError>