Decode the highest scoring sequence of tags.

potentials A [batch_size, max_seq_len, num_tags] tensor of unary potentials.
transition_params A [num_tags, num_tags] matrix of binary potentials.
sequence_length 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.