Synchronize consider_as_space() with HarfBuzz’s is_default_ignorable()
It seems that consider_as_space()
relies too much in Unicode general categories and results in characters like U+06DD not having fallback because it has Cf general category. I think HarfBuzz’s is_default_ignorable()
is a better source of such information.
Or may be Pango should switch to shaping then doing fallback, like Chrome does.
cc @behdad.
Edited by Khaled Hosny