constructor(hiddenLayerSizesOrModel) {
    if (hiddenLayerSizesOrModel instanceof tf.LayersModel) {
      this.policyNet = hiddenLayerSizesOrModel;
    } else {
      this.createPolicyNetwork(hiddenLayerSizesOrModel);
    }
  }
Constructor of PolicyNetwork.

@param {number | number[] | tf.LayersModel} hiddenLayerSizes
  Can be any of the following
  - Size of the hidden layer, as a single number (for a single hidden
    layer)
  - An Array of numbers (for any number of hidden layers).
  - An instance of tf.LayersModel.