如何将xlnet作为嵌入层置于其他模型前
### Feature request

我想将预训练模型xlnet作为嵌入层添加到bilstm-CRF前，如何作为一个嵌入层加入到模型的构建当中。比如说，我现在用bert4keras框架搭建好了bert-Bilstm-Crf模型，我想将bert替换为xlnet，将xlnet作为模型的嵌入层，这样可不可以？？？
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    def bert_bilstm_crf(config_path,checkpoint_path,latm_units,drop_rate,learning_rate):      # 构建模型的结构
       -----------------------------------------------------------------------------------以下关于bert的内容是否可以替换
         bert=build_transformer_model(                              #BERT加载权重
                    config_path=config_path,
                    checkpoint_path=checkpoint_path,
                    model='bert',
                    return_keras_model=False
                )
        x=bert.model.output       #[batchsize,seq_len,768] 
        x=keras.layers.Bidirectional(
            keras.layers.LSTM(         #加入lstm模型
                latm_units,
                kernel_initializer='he_normal',    #初始化规则
                return_sequences=True
        )
        )(x)    #[batchsize,seq_len,lstm_units*2]

### Motivation

修改关于ner方面的问题

### Your contribution

解决模型构建的问题
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