For now measurements are aggregated by SumFactory, but we will add support in the future for private measurements aggregation.

Also:
  1. Change state to OrderedDict (from tuple).
  2. Change default zeroing norm order from np.inf to 2 for ease of transition between ZeroingFactory and ZeroingClippingFactory (which must use 2-norm), and use tf.linalg.global_norm if norm order is 2, for efficiency.
PiperOrigin-RevId: 339908232