* [dy2static] bugfix: make stop_gradient a cache key
1. make stop_gradient cache key in dy2static.

* fix ci errors

* fix ci error

* fix ci error

* fix ci error

* add enable_to_static and drop some methods of ProgramTranslator

* fix code style

* fix cant import enable_to_static and update unitest

* change unitest and rollback code of PT

* fix can't import as of utils

* roll back PT

* fix roll back

* add some unitest

* add unitest and fix codestyle bug in api.py

* finish all unitest

* remove ProgramTranslator

* fix code style

* restore test_program_translator

* api.py remove get_func

* TestDygraphToStaticCode

* fix check_type and import err

* roll back PT without getcode

* roll back pt with get_code

* convert_to_static

* fix import __all__

* [CodeStyle][py2][U008] remove unnecessary args in `super()`

* remove remained args

* revert changes in test_pylayer_op

* Revert "revert changes in test_pylayer_op"

This reverts commit ff185a9ae738afac3b0264f61bde6c6b7f72e7c4.

* revert some changes in example code

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

GridGenerator model failed because the output shape of `linspace` is (-1). The reason is that C++ InferShape fixes the shape to (-1): 

https://github.com/PaddlePaddle/Paddle/blob/5da3d514ebaa6fffd48c4a2e6bb5b16268dae92e/paddle/fluid/operators/linspace_op.cc#L49

We cannot set the shape in C++ infer shape because this Tensor may not be initialized during compile time, but when input `num` of `linspace` is an integer, we know the shape at compiler time. This PR simply set the shape in Python and add GridGenerator as unittest.