message: Updating scatter semantics to include an invariant.
diff: @@ -2248,6 +2248,9 @@ The arguments of scatter should follow these constraints:
  - `inserted_window_dims` must be in ascending order, not have any repeating
  dimension numbers, and be in the range `[0, operand.rank)`.
  +- `operand.rank` must equal the sum of `update_window_dims.size` and
  + `inserted_window_dims.size`.
  +
  - `scatter_dims_to_operand_dims.size` must be equal to
  `scatter_indices`[`index_vector_dim`], and its values must be in the range
  `[0, operand.rank)`.
  