[tf.data] Marking dataset ops that consume a dataset without an iterator as...

[tf.data] Marking dataset ops that consume a dataset without an iterator as stateful to make sure they are not prune from the graph in case their output is not used.

This is a conservative approach to guarantee that any side-effects of the op are carried out.

This CL also reverts a previous (incomplete) solution to the same problem.

PiperOrigin-RevId: 233663631