Computes the unnormalized score for a tag sequence.

inputs A [batch_size, max_seq_len, num_tags] tensor of unary potentials to use as input to the CRF layer.
tag_indices A [batch_size, max_seq_len] matrix of tag indices for which we compute the unnormalized score.
sequence_lengths A [batch_size] vector of true sequence lengths.
transition_params A [num_tags, num_tags] transition matrix.

sequence_scores A [batch_size] vector of unnormalized sequence scores.