* support save_inference_model in program_translator test=develop

* fix compatibility with OrderedDict.values() in python3 test=develop

* synchronized random_seed test=develop

* Polish Error Message test=develop

* [Dy2Stat] Add test for bert pretraining. 

* Construct fake data. 

* Synchronous random seed of program. 

* support to train in static

* support to independent decorator

* remove in_dygraph_mode condition in ProgramTranslator

* fix import param_guard and add train/eval test=develop

* Modify into ShareVarsFromScope and rm __all__ in partial_program 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.

* 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

* Simplify code for gast.If in is_control_flow_to_transform.
* Move IsControlFlowVisitor to file utils. 
* Don't use convert_call for build-in func in CallTransformer. 
* Optimize api is_control_flow_to_transform. 
* Polish the document of IsControlFlowVisitor.

Fix bug in convert_call because difference exists between python3 and python2. test=develop (#23966)

* [Dy2Stat]Support recursive call.

* Remove Redundant decorator to pass the Py35 unittest temporarily.

[Dy2stat] Add Test and Example Code for Different Access to ProgramTranslator and Fix Related Bug (#23958)

To prepare for publishing APIs, I added tests for that we can access dy2stat through:

@fluid.dygraph.declarative
@fluid.dygraph.jit.declarative
fluid.dygraph.ProgramTranslator()
fluid.dygraph.dygraph_to_static.ProgramTranslator()
fluid.dygraph.dygraph_to_static.program_translator.ProgramTranslator()

It surprised me that we had bugs on those different usages. I have fixed them.

I also added example codes for these new APIs

This PR also pulls my current PR https://github.com/PaddlePaddle/Paddle/pull/23880, so the PR history is long. For reviewer information, you could review this PR after https://github.com/PaddlePaddle/Paddle/pull/23880 is merged

1. Rename Dygraph To Static Decorators to declarative
2. dygraph_to_static_func is still using in some training tests, I cannot delete it now.
3. Add some API docs

* Move BasicApiTransformer to a separate file. test=develop

* Fix a bug: A api in module is not a real dygraph api in dygraph_to_static. test=develop

* Spport transform two independed function in dygraph_to_static_output test=develop

* fix unittest error test=develop

* Refine mechanism of calling outer function test=develop

* fix typo test=develop

This CR makes two changes:

1. In old loop_transformer, if a class variable, such as "self.a, foo.bar" is a loop var, the Dy2stat will fail because `def func(self.foo)` is not legal syntax. We support class variable by renaming.

2. After https://github.com/PaddlePaddle/Paddle/pull/22892 is merged, we can support `while x < 10` in dygraph. I enable those tests in corresponding Dy2stat

* Add unitTest for `Tensor==constant` for ifElse in dygraph2static test=develop

1. Add data_layer_not_check because it is needed in dygraph_to_static where input can be variable size
2. Remove warnings in static analysis because python cannot do exact static analysis

* Remove Read-Only Basic Type Variable in loop_vars

test=develop

* Put class support in loop for future thing

test=develop

* Modify based on reviewer's comment

test=develop

* Support Parameter type determination test=develop

1. Add Decorator 'dygraph_to_static_program'
2. Add corresponding ProgramTranslator.get_program
3. Add ProgramTranslator.save_inference_model
4. Modified some warning information of dy2stat
5. Change program cache to contain startup_program because for users who gets program to run, they may like to initialize startup program

* add unittest test=develop

* add function cache test=develop

This PR does exact the thing as the title. The reason is that we plan to develop 4 decorators

"dygraph_to_static_code"
"dygraph_to_static_program"
"dygraph_to_static_func"
"dygraph_to_static_output"

 The 4 decorators will emphasize different part when translating dygraph to static graph. Decorator name "dygraph_to_static_graph" is too big for the function it implements.

As the title, we add decorator "dygraph_to_static_code", and add related "get_code", "get_func", "get_output" for ProgramTranslator. Next step will be adding "dygraph_to_static_program"

1. Rename AutoTracer to ProgramTranslator
2. Rename cached_program to program_cache
3. Remove some functor style __call__
4. Dict key should be string but not hash code of string

As the title

* Support to use external function test=develop

* refine the parms of ast_to_func test=develop

1. Add support for Break and Continue in Dygraph to Static
2. Also add support for gast.Not in NodeTestTransformer
3. Also add support for logical op transformation in LoopTransformer

* Support and/or in controlFlow if test=develop