src/transformers/models/lxmert/modeling_tf_lxmert.py/TFLxmertPooler/call
class TFLxmertPooler:    def call(self, hidden_states):
        # We "pool" the model by simply taking the hidden state corresponding
        # to the first token.
        first_token_tensor = hidden_states[:, 0]
        pooled_output = self.dense(first_token_tensor)
        return pooled_output