[PaddlePaddle Hackathon] 第53题 (#1114)

* finish develop bigbird

* add bigbird unitest

* fix doc

* remove BigBirdLMhead

* remove BigBirdLMhead and fix bugs

* remove BigBirdForQuestionAnsweringHead class

* add doc

* update document tables

* 删除未使用字段

Co-authored-by: yingyibiao <yyb0576@163.com>

Author: iverxin

docs/model_zoo/transformers.rst

@@ -447,7 +447,6 @@ Transformer预训练模型汇总
 Transformer预训练模型适用任务汇总
 ------------------------------------
 
-
 +--------------------+-------------------------+----------------------+--------------------+-----------------+-----------------+
 | Model              | Sequence Classification | Token Classification | Question Answering | Text Generation | Multiple Choice |
 +====================+=========================+======================+====================+=================+=================+
@@ -457,7 +456,7 @@ Transformer预训练模型适用任务汇总
 +--------------------+-------------------------+----------------------+--------------------+-----------------+-----------------+
 |BERT_               | ✅                      | ✅                   | ✅                 | ❌              | ✅              |
 +--------------------+-------------------------+----------------------+--------------------+-----------------+-----------------+
-|BigBird_            | ✅                      | ❌                   | ❌                 | ❌              | ❌              |
+|BigBird_            | ✅                      | ✅                   | ✅                 | ❌              | ✅              |
 +--------------------+-------------------------+----------------------+--------------------+-----------------+-----------------+
 |ConvBert_           | ✅                      | ✅                   | ✅                 | ✅              | ✅              |
 +--------------------+-------------------------+----------------------+--------------------+-----------------+-----------------+