If HarfBuzz is enabled, the reverse character map generation now considers
GSUB entries when looking for glyphs that correspond to a code point.
* src/autofit/afadjust.c (af_all_glyph_variants_helper,
af_all_glyph_variants) [FT_CONFIG_OPTION_USE_HARFBUZZ]: New functions.
(af_reverse_character_map_new) [FT_CONFIG_OPTION_USE_HARFBUZZ]: Call new
code.