code: def feed_forward_builder(name, hidden_dim, activation, trainable=True):
      
      def _feed_forward_builder(x):
          return FeedForward(
              units=hidden_dim,
              activation=activation,
              trainable=trainable,
              name=name,
          )(x)
      return _feed_forward_builder
docs: Get position-wise feed-forward layer builder.
  
      :param name: Prefix of names for internal layers.
      :param hidden_dim: Hidden dimension of feed forward layer.
      :param activation: Activation for feed-forward layer.
      :param trainable: Whether the layer is trainable.
      :return: