code: def downstream_index_dinf(dinfdir_value, i, j):
          
          down_dirs = DinfUtil.dinf_downslope_direction(dinfdir_value)
          down_coors = []
          for dir_code in down_dirs:
              row, col = D8Util.downstream_index(dir_code, i, j)
              down_coors.append([row, col])
          return down_coors
docs: find downslope coordinate for Dinf of TauDEM
          Args:
              dinfdir_value: dinf direction value
              i: current row
              j: current col
  
          Returns:
              downstream (row, col)s