"self" tensor are included in the reduction
Example:
  >>> x = torch.empty(5, 3).fill_(2)
  >>> t = torch.tensor([[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]], dtype=torch.float)
  >>> index = torch.tensor([0, 4, 2, 0])
  >>> x.index_reduce_(0, index, t, 'prod')
  tensor([[20., 44., 72.],
          [ 2.,  2.,  2.],
          [14., 16., 18.],
          [ 2.,  2.,  2.],
          [ 8., 10., 12.]])
  >>> x = torch.empty(5, 3).fill_(2)
  >>> x.index_reduce_(0, index, t, 'prod', include_self=False)
  tensor([[10., 22., 36.],
          [ 2.,  2.,  2.],
          [ 7.,  8.,  9.],
          [ 2.,  2.,  2.],
          [ 4.,  5.,  6.]])
