TF BART models - Add cross_attentions to model output and fix cross-attention head masking (#10699)

* Add cross_attn_head_mask to BART

* Fix cross_attentions in TFBart-like models

* This commit enables returning of `cross_attentions`
for TFBart-like models

* It also fixes attention head masking in cross-attenion module

* Update TF model templates

* Fix missing , in TF model templates

* Fix typo: congig -> config

tests/test_modeling_tf_blenderbot.py

@@ -146,6 +146,7 @@ def prepare_blenderbot_inputs_dict(
     decoder_attention_mask=None,
     head_mask=None,
     decoder_head_mask=None,
+    cross_attn_head_mask=None,
 ):
     if attention_mask is None:
         attention_mask = tf.cast(tf.math.not_equal(input_ids, config.pad_token_id), tf.int8)
@@ -161,6 +162,8 @@ def prepare_blenderbot_inputs_dict(
         head_mask = tf.ones((config.encoder_layers, config.encoder_attention_heads))
     if decoder_head_mask is None:
         decoder_head_mask = tf.ones((config.decoder_layers, config.decoder_attention_heads))
+    if cross_attn_head_mask is None:
+        cross_attn_head_mask = tf.ones((config.decoder_layers, config.decoder_attention_heads))
     return {
         "input_ids": input_ids,
         "decoder_input_ids": decoder_input_ids,
@@ -168,6 +171,7 @@ def prepare_blenderbot_inputs_dict(
         "decoder_attention_mask": decoder_attention_mask,
         "head_mask": head_mask,
         "decoder_head_mask": decoder_head_mask,
+        "cross_attn_head_mask": cross_attn_head_mask,
     }