Always set explicit HarfBuzz buffer direction

Always set explicit HarfBuzz buffer direction

If no direction was given by the caller, I assume the text will be drawn
left to right, if this is not the case then callers must provide
sensible direction. Letting HarfBuzz guess the direction is not
appropriate since shaping and drawing must use the same direction.

Also move hb_buffer_guess_segment_properties() call to the end, so it
only guessing unset properties, until we completely get rid of it.