Decode the highest scoring sequence of tags.
crf_decode(potentials, transition_params, sequence_length)
A [batch_size, max_seq_len, num_tags] tensor of unary potentials.
A [num_tags, num_tags] matrix of binary potentials.
A [batch_size] vector of true sequence lengths.
decode_tags: A [batch_size, max_seq_len] matrix, with dtype `tf.int32`. Contains the highest scoring tag indices. best_score: A [batch_size] vector, containing the score of `decode_tags`.