1. To make ProgramTranslator to support `assert` grammar, this PR adds `assert` python API and C++ code. 

2. Fix a bug: graph_pattern_detector.h #include <gtest/gtest_prod.h> but didn't declared dependency at CMakeLists, which can cause single build failure.

3. Refactoring `Formatter` in print_op to make it reusable and reuse the formatter to print in assert op.

目前在while_loop的执行过程中，loop_vars中的变量在每次的循环中都会进行拷贝，但是LoDTensorArray类型的变量在while循环体中已经完成了读/写的操作，即完成了更新，此时在进行拷贝属于冗余的操作，故该PR跳过每次循环中loop_vars中LoDTensorArray类型的变量的复制过程。

在PaddleCV/ocr_recognition/atention模型的预测过程中进行性能测试：
|性能|with this PR|without this PR|提升|
|---|---|---|---|
|速度|4957.4ms|4978.47ms|0.4%|

* fix error message, test=develop

* add unittest, test=develop

* API/OP (margin_rank_loss, nce, row_conv, glu, positive_negative_pair) error message enhancement, test=develop

* add unittest for glu, test=develop

* Replace dygraph_to_static_func with @declarative or program_translator.get_func in test_list.py

* Add comments in ConditionalBlock.

* Support list pop last item. 

* Support pop the i-th item. 

* Support an empty tensor array as Input in assign op and set the kernel type is float.

* update dygraph.rnn import

* update dygraph.rnn import

* change unit to cell

* fix math equations

* fix math equations

* fix examples

* remove unused import

* fix examples

* fix error info for rnn related api

* passed local test, test=develop

* double check the code

* double check the code, test=develop

* update 'shape' check in RNNCell, test=develop

* add long dtype to RNNCell

* fix long type in python3
Co-authored-by: NXingWu01 <wuxing@iie.ac.cn>

test=develop

* add timeout and http store in communication, add revert and confirm in fleet
* test=develop

* Move complex into dir incubate, test=develop

* Fix imports, test=develop

* Fix docs, test=develop

* Forbid import functions from paddle.incubate directly, test=develop

Add the pslib graph batch reader mode, add the test case for this change

* Support LoDTensorArray for slice op.
* Support read elements of list in dygraph_to_static
* Fix infershape add test for infershape.
* Support Tensor for Attr(starts) and Attr(ends). 
* Use new interfaces in VarTypeInference. 

* Rename internal gradient variables in multiple backward
* so that they have different names with previous backward
* For example:
*  y = x * x, grad = fluid.gradients(fluid.gradients(y, x) + y * y, x)
* In second-time backward, gradient variable names of partial
* forward network (y * y) may be have same names with first-time
* fluid.gradients(y, x).

test=develop

fix kron_op: when only one input needs gradient

* enhance add_position_encoding error message, test=develop

* enhance warpctc & scaled_dot_product_attention error message, test=develop

* modified error message and ctest of scaled_dot_product_attention, test=develop

* add unbind pyhon api. test=develp

* update local data preprocess doc

* update for 2.0 QAT

test=develop

test=document_fix

* update benchmark data

test=develop

test=document_fix
Co-authored-by: NWojciech Uss <wojciech.uss@intel.com>

* Add complex layer for transpose & matmul, test=develop

* Tiny fixes in doc, test=develop

* Fix docs, test=develop

* remove double registery for pyramid_hash op

* add noavx_axpy and noavx_axpy_noadd

test=develop

test=develop

* add reshape in paddle.complex, test=develop
* fix typos in paddle.complex.kron's comment, fix unittest, test=develop

* test=develop fix generate_proposals

* add print transformer & unify print format, test=develop

* remove using of dygraph_to_static_func, test=develop

* remove python stdout capture, test=develop

* fix compatibility problems for PY2, test=develop

* fix detail error, test=develop

* fix type analysis bug, test=develop

* fix print tuple compatible error in PY2, test=develop

* replace get_func to declarative, test=develop

* fix detail bug, test=develop

* fix some detail problems, test=develop

* change visit_call in print transformer, test=develop

* add trace op, test=develop

* Optimized the implementation of trace op, test=develop

* fix a bug of include in trace_op.h, test=develop

* move trace API from creation to math, test=develop

* modified en doc. test=develop

* add complex trace api

* add complex sum api, test=develop

* modified en doc of complex sum and trace, test=develop

* modified doc and trace API, test=develop

* modified en doc of trace and sum, test=develop

* modified comment in complex kron API, test=develop

* OP Should Not Have Unused Input, test=develop

* add GetExpectedKernelType, test=develop

* add batch fc op, test=develop

* add batch_fc_op, test=develop

* fix untest, test=develop

* rm check_dygraph, test=develop

* fix comment, test=develop

* fix comment, test=develop