The indices of scatterElements can't point to the same output location

[BruceDai]

1. Refer to DML_SCATTER_OPERATOR_DESC

If two output element indices overlap (which is invalid), then there's no guarantee of which last write wins.

2. Refer to ScatterElementsUpdate

Inputs:

2: indices ... If multiple indices point to the same output location then the order of updating the values is undefined.