Before, we were just checking the use_category(). This detects as
halant a ligature that had the halant as first glyph (as seen in
NotoSansBalinese.) Change that to use the is_ligated() glyph prop
bit. The font is forming this ligature in ccmp, which is before
the rphf / pref tests. So we need to make sure the "ligated" bit
survives those tests. Since those only check the "substituted" bit,
we now only clear that bit for them and "ligated" survives.
Fixes https://github.com/behdad/harfbuzz/issues/180
Behdad Esfahbod