class_docstr: BeamSearchDecoderMixin contains the common methods for
  BeamSearchDecoder.
  
  It is expected to be used a base class for concrete
  BeamSearchDecoder. Since this is a mixin class, it is expected to be
  used together with other class as base.
code: def output_size(self):
      # Return the cell output and the id
      score_size = (
          tf.TensorShape(
              [self._beam_width, self._rnn_output_size()[-1]]
          )
          if self._output_all_scores
          else tf.TensorShape([self._beam_width])
      )
      return BeamSearchDecoderOutput(
          scores=score_size,
          predicted_ids=tf.TensorShape([self._beam_width]),
          parent_ids=tf.TensorShape([self._beam_width]),
      )
  
imports: import collections
  import numpy
  import tensorflow
  from tensorflow_addons import options
  from tensorflow_addons.seq2seq import attention_wrapper
  from tensorflow_addons.seq2seq import decoder
  from tensorflow_addons.utils import keras_utils
  from tensorflow_addons.utils.resource_loader import LazySO
  from tensorflow_addons.utils.types import FloatTensorLike, TensorLike, Number
  from typeguard import typechecked
  from typing import Callable, Optional
label_desc: Use image node_id 5 for calling the BeamSearchDecoderMixin obj's underlying member method code with example usage: obj.output_size() and returns: BeamSearchDecoderOutput