A continuing partial implementation of RFC "Random numbers in TensorFlow 2.0"...

A continuing partial implementation of RFC "Random numbers in TensorFlow 2.0" (https://github.com/tensorflow/community/pull/38):

In this change:
- XLA kernel (TF-XLA bridge) for op `StatefulStandardNormalV2` with ThreeFry algorithm.

To be done:
- ops for other distributions;
- other RNG algorithms;
- batch seeds;
- initializers ('RandomUniform', etc.);
- changing `non_deterministic_seed`'implementation to be an op, and other changes to make most code in stateful_random_ops.py tf.function-compatible.

PiperOrigin-RevId: 236699104