Adding type hints for TFXLnet (#19344)
* Added type hints for TF: XLNet
* Added type hints for TF: XLNet
* Added type hints for TF: XLNet
* Added type hints for TF: XLNet
* Added type hints for TF: XLNet
* Added type hints for TF: XLNet
* Add type hints for XLnet (TF)
* Added type hints for XLnet (TF)
* Update src/transformers/models/xlnet/modeling_tf_xlnet.py
