[HarfBuzz] Malayalam reph positioning

[Suresh P]

Hi,

The Malayalam reph is to be placed logically in the beginning of 
syllable and positioned above-base. But it is now seen at the end of the 
syllable even as hb-ot-shape-complex-indic.cc says:

/* There are two kinds of characters marked as Repha:
      * - The ones that are GenCat=Mn are already positioned visually, 
ie. after base. (eg. Khmer)
      * - The ones that are GenCat=Lo is encoded logically, ie. 
beginning of syllable. (eg. Malayalam)
      *

Meanwhile old harfbuzz and pango indic shaper get it right as above-base.

- suresh