fix assisted decoding assistant model inputs (#27503)
* fix assisted decoding attention_cat
* fix attention_mask for assisted decoding
* fix attention_mask len
* fix attn len
* Use a more clean way to prepare assistant models inputs
* fix param meaning
* fix param name
* fix assistant model inputs
* update token type ids
* fix assistant kwargs copy
* add encoder-decoder tests of assisted decoding
* check if assistant kwargs contains updated keys
* revert test
* fix whisper tests
* fix assistant kwargs
* revert whisper test
* delete _extend funcs
