* [API Clean]Clean __all__ to avoid exposing usless API

* fix import

* fix typo

* remove tracedLayer unittest

* [Dy2St] refactor convert_print to display Tensor in compile time

* [Fluid Clean]Migrate utils files and delete dygraph_to_static dir

* fix setup.py.in

* fix import

* fix unittest

* fix code style

* fix unittest

* [Fluid clean]Migrate base/call/print et.al transformer into paddle.jit

* fix phi kernel

* Revert "fix phi kernel"

This reverts commit eff8891c7efda6e49799edbcaef2ca50379d50ef.

* [Fluid Clean]Migrate if/while/return/break transformer into paddle.jit

* migrate call_transformer

* migrate call_transformer

* [Fluid Clean] Migrate program_translate.py/jit.py into paddle.jit dir

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* Add TypeHint Transformer

* add unittest for typehint transformer

* [Dy2Static] Remove GradTransformer
1. fix einsum infershape bugs.
2. remove grad_transformer and unify paddle.grad and paddle.static.gradient.
3. add dygraph_and_dy2static_only decorator for dy2static.

* fix bugs

* rename

* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

[BugFix] fixed a bug in decorator transformer, it can not analyze decorator with params correctly (#46055)

* fix deco call

* add raise

* add test

* add warn, fix paddle api

* fix error type

* fix coverage

* support deco

* fix deco ast type

* arg_str

* 1

* support callable deco

* code style

* codestyle

* test_error

* fix decos in another file

* recover conflict codes

* convert_call support staticmethod for class.

* while support for python container.
It is convenient to convert more dynamic graph codes into static graphs.

* cond support python container

* add unittest for staticmethod convert_call

* fix bugs

* add unittest for item interface

* fix bugs

* change to np.testing.assert_allclose

* code format

* fix comments.

* code format

* 1. make list transformer into jit form.
2. fix some bugs in tensor_array, such as append.
3. enhance the function analysis visitor to recognize push/pop.
4. add setter/getter helper to deal with 2+ name sets.

* fix ci errors:
1. add to_tensor_array logic in convert_cond
2. fix IfExpr error.
3. fix erros while return_names or push_pop_names is None
4. fix slice error in a[i]=1 where a is tensor_array
5. add pop interface in Variable

* change NameVisitor to FunctionScopeAnalysis

* polish the logic of undefined var in while_loop. create vars after body execution

* replace old NameVisitor in while and fix all CI

* Togather with CreateVariableTransformer

* add create_variable_transformer

* fix bugs

* merge

* fix some error, TODO: ForNodePreTransform ahead

* merge for unite PR

* fix conflict with base_transformer PR

* fix ci errors, fix [for i in range()] error

* fix according to code review

* add support for control flow block analysis

* move FunctionNameLivenessAnalysis into utils

* pass test_ifelse.py

* remove duplicate data_layer_not_check

* pass the test_ifelse.py

* fix unittest error .

* fix all ci error in first version

* temporay disable CreateVariableTransformer

* fix ci errors

* fix function name liveness analysis bugs

* modifty def cond

* fix

* fix ci error - v2

* fix by code review

* change return_name_ids -> return_name

* Add BaseTransformer for dy2st error message

* Fix return_transformer error

* Polish dy2st error info in runtime

* Fix UT error

* Polish runtime error code

* Refine ifelse early return

[Dy2Stat]Add apply_optimization for @to_static and remove BreakTransformOptimizer by default (#43320)

* [Dy2Stat]Add apply_optimization for @to_static and remove BreakTransformOptimizer by default

* fix unittest

* integrated gast library

* integrated gast library

* fix unittest and remove ast2.py

* remove 'gast' from __all__ in __init__.py

* add copyright in other files

* fix copyright

This PR made these changes to support double grad:

1. Translate `paddle.grad` to `paddle.static.gradients` to support double grad for dy2stat.
2. Fix IfElseTransformer bug which may not change value if "Store before Load" variable is in "Store" statement is in IfElse conditional statement
3. Add `DOut` to support double grad variables in `run_program_op`
4. Add support for renaming for double grads for `jit.save/load`

* Join break cond with while cond

* remove usless code

* refine the if code

* Split into BreakTransfromOptimizer

* add BreakTransformOptimizer in ast_transformer

* add more comment

* refine code of DygraphToStaticAst

* add __init__ function

* Add env value to  log to stdout; 2.Add logger name

* Optimize log messages in dygraph-to-static

* Replace logging.warn and warnings.warn with logging_utils.warn

* [Dy2Stat] Add debugging and logging mechanism for dygraph to static. 

* Remove TransformerError temporarily. 

* import mock in PY2, from unittest import mock in PY3. test=develop

* Expose interfaces set_code_level and set_verbosity in paddle.jit, fix doc of the two interface. 

* polish doc of set_verbosity and set_code_level. 

* add cast transform and its UT for dygraph_to_static. 

This PR added basic support for 'return' grammar in dy2stat. It supports the control flow of 'return'.

The basics idea is using a return value variable to store the early return statements and boolean state variables with if-else to skip the statements after the return statements.

**This PR is very basic support. There are some corner cases I didn't develop/test**. For example, 'return None', 'return different length of variables', 'return non-tensor and tensor together', 'no return statement'. **These corner cases will be done in my next PRs**. Target date is this week.

**Note**: 
1. for the unit test, I changed test_program_translator.py because the StaticCode of `dyfunc_with_if_else` will change. To guarantee the correctness of `dyfunc_with_if_else`, I also run it in `TestRecursiveReturn` in test_return.py.

2. I commented the early return code in bert_dygraph_model.py because 'return different length of variables' is unsupported now. I also know that there are some other models used early return and we didn't enable it in the unit test. I will add support for it in next PRs and then re-enable those tests.

* Refine caches of converting func test=develop

* fix if statement test=develop

* refine cache code test=develop

* rm unuse import statement test=develop

* Polish code comment test=develop

* cast var in convert_logical_XX. 

* Add convert_ifelse function in convert_operators.py  

* Add logical_transformer. Remove LogicalTransformer from loop_transformer.py 

* Revert modified tests in PR24799(convert_while_stmt). 

* Comment and modify code that doesn't support `return` statement. 

* Remove unnecessary class: MergeAssignTransformer, NodeTestTransformer and IfConditionVisitor in ifelse_transformer. 

Add assert grammar for ProgramTranslator

* 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

* 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

* [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