Breaking change: Rename `tf.contrib.distributions.Independent` parameter from

`reduce_batch_ndims` to `reinterpreted_batch_ndims`. Also change default;
`reinterpreted_batch_ndims` default has semantics of `tf.layers.flatten`, i.e.,
all batch dimensions except the first (batch axis 0) are interpretted as being
part of the event.

PiperOrigin-RevId: 173729585