Fetches the HarfBuzz.direction_t of a script when it is
set horizontally. All right-to-left scripts will return
#HB_DIRECTION_RTL. All left-to-right scripts will return
#HB_DIRECTION_LTR.
Scripts that can be written either right-to-left or
left-to-right will return #HB_DIRECTION_INVALID.
Fetches the HarfBuzz.direction_t of a script when it is set horizontally. All right-to-left scripts will return #HB_DIRECTION_RTL. All left-to-right scripts will return #HB_DIRECTION_LTR.
Scripts that can be written either right-to-left or left-to-right will return #HB_DIRECTION_INVALID.
Unknown scripts will return #HB_DIRECTION_LTR.