Get lookup table for VQ bottleneck.

def get_vq_codebook(codebook_size, hidden_size):
  """Get lookup table for VQ bottleneck."""
  with tf.variable_scope("vq", reuse=tf.AUTO_REUSE):
    means = tf.get_variable(
        name="means",
        shape=[codebook_size, hidden_size],
        initializer=tf.uniform_unit_scaling_initializer())

    ema_count = tf.get_variable(
        name="ema_count",
        shape=[codebook_size],
        initializer=tf.constant_initializer(0),
        trainable=False)

    with tf.colocate_with(means):
      ema_means = tf.get_variable(
          name="ema_means",
          initializer=means.initialized_value(),
          trainable=False)

  return means, ema_means, ema_count