cherry-pick,fix optimizer.state_dict and LRScheduler.state_dict to save/load dygraph

add new API:LambdaDecay,test=develop 

* CHERR-PICK1.8,add base class of LearningRateEpochDecay, and API: MultiStepDecay, and API: StepDecay,test=release/1.8

* fix unittest to add coverage,test=develop

* fix bug of prelu when rank not equal 4, test=develop

* fix prelu inference, test=develop

* fix api, test=develop

* fix shape when mode is chennel, test=develop

* remove debug code, test=develop

* add unittest, test=develop

fix sample code error of fluid.dygraph.NaturalExpDecay

添加loss自适应的学习率衰减策略。

* add clean up; test=develop

* add import; test=develop

* Append scale for static runner outputs (#24627)

* add scale for static runner outputs, test=develop

* fix import relation, test=develop

* remove len limit, test=develop

* remove imperative data loader place limit, test=develop (#24641)

* fix convert call globals_funcs test=develop

* add import statement test=develop

* [Dy2Stat] Add test for ptb model. (#24076)

* [Dy2Stat] Add test for ptb model. test=develop

* Simplify code for gast.If in is_control_flow_to_transform. test=develop

* Move IsControlFlowVisitor to file utils. test=develop

* Don't use convert_call for build-in func in CallTransformer. test=develop

* Optimize api is_control_flow_to_transform. test=develop

* Polish the document of IsControlFlowVisitor. test=develop

* Use declarative instead of dygraph_to_static_func. test=develop

* [dy2static] Add print transformer and unify print format (#24068)

* 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

* [dy2static] Support for static graph training with @declarative decorator (#24259)

* 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

* [Dy2Stat] Optimize loop cond (#24049)

* 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.

* revert modification from #24259

* [dy2stat]Support save_inference_model in program_translator (#24353)

* 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

* Fix bug with `if Tensor` in is_control_flow (#24433)

* fix bug with `if Tensor` in is_control_flow test=develop

* remove continue test=develop

* Revert "[dy2static] Add print transformer and unify print format (#24068)"

This reverts commit 09dd0190.

* Revert "[dy2static] Add print transformer and unify print format (#24068)"

This reverts commit 09dd0190.

* fix sample code in sava_inference_model test=develop
Co-authored-by: Nliym27 <33742067+liym27@users.noreply.github.com>
Co-authored-by: NChen Weihang <chenweihang@baidu.com>

* add enable_imperative, disable_imperative; test=develop

* add unitest; test=develop

* polish example; test=develop

* fix CrossEntropyLoss op en doc, test=develop

* delete unittests,test=release/2.0

* copy api from paddle to paddle.fluid, test=develop

* fix optest, test=develop

* adapt old version pretrain model load, test=develop

* fix infer error & multiple input error, test=develop

* Init complex number neural network, test=release/2.0

* Improve doc writing

* Fix elementwise add & sub

* Fix elementwise mul act

* a) add ut for complex variable; b) remove arg act in elementwise_ops

* Add trainable_statistics in attr for batch_norm
* Unifying behavior of dynamic graph and static graph

chery-pick from the pr#23978

* [Cherry-pick][dy2static]Support recursive call (#23900)
  * Support recursive call.

  * Remove Redundant decorator to pass the Py35 unittest temporarily.

* [Cherry-pick]Fix bug in convert_call because difference exists between python3 and python2. (#23966 )

[Dy2stat] Add Test and Example Code for Different Access to ProgramTranslator and Fix Related Bug (#23958) (#23963)

Cherry pick of 23958

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

* [Cherry-pick Release/2.0] remove redundant visit func, test=develop (#23877)

* [Cherry-pick Release/2.0] [dy2static]Fix a bug of is_dygraph_api and move BasicApiTransformer to a separate file(#23923)

* 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
Co-authored-by: NChen Weihang <chenweihang@baidu.com>

test=release/2.0

* fix if logic in dygraph, test=develop

* fix bug, test=develop

* Spport transform two independed function in dygraph_to_static_output test=develop

* fix unittest error test=develop

* err msg enhance for PRelu

* add ut
test=develop

* err msg enhance for GRUUnit

* add ut
test=develop

* err msg enhance for Embedding

* add ut
test=develop

* err msg enhance for BilinearTensorProduct
test=develop

* rebase dev
test=develop

* add ut
test=develop

* Refine mechanism of calling outer function test=develop

* fix typo test=develop

test=develop

* add instance_norm op for dygraph, test=develop

* add error message, test=develop

* add LayerList insert and extend
test=develop

* add index range check
test=develop

* add sample codes
test=develop

* refine sample code
test=develop

* API(to_variable/save_dygraph) error message enhancement

* error message enhancement for Conv2DTranspose, test=develop

* fix error_message, test=develop