[Indic] Apply 'cfar' for Khmer

Mark stuff after a pre-base reordering Ro 'cfar'.  Used in Khmer.
This allows distinguishing the following cases with MS Khmer fonts:

  U+1784,U+17D2,U+179A,U+17D2,U+1782
  U+1784,U+17D2,U+1782,U+17D2,U+179A