[ft] Add API to notify that hb_font_t changed New API: - hb_ft_hb_font_changed() Mostly reverts 56e0ff9ea129aa91dfcc746cd61f8cbbc427dba7 Related https://github.com/harfbuzz/harfbuzz/issues/2270 Fixes https://github.com/harfbuzz/harfbuzz/issues/3619