Validate ScatterND index depth (#32034)
This pull request improves input validation for the `ScatterND` operator
and adds a corresponding unit test to ensure that invalid input is
properly rejected.
Input validation:
* Added a check in `scatter_nd.h` to ensure that the last dimension of
the `indices` tensor is at least 1, returning an error if it is not.
Testing:
* Added a unit test in `scatter_nd_op_test.cc`
(`ScatterND_rejects_zero_index_depth`) to verify that the operator
rejects `indices` tensors with a zero-sized last dimension.
