The appearance of letterspacing with scripts with cursive connections
is poor, so we simply disable letterspacing for those scripts. There
may be some cases where some form of letterspacing is desirable, but
this gives the highest likelihood that the final result will be good
without requiring additional work from clients.

Bug: 21935803
Change-Id: Ie25266249ac3a2605aa89ef5132e8edbe3a06d35