* 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

* test=release/1.8, add index sample

test=release/1.8, test=document_fix

* 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 beam_search infershape, test=develop

* fix beam search op unittest, test=develop

fix sample code error of fluid.dygraph.NaturalExpDecay

Fix the bug for elementwise_div op, when the first var is scalar; Use the shape 1 replace the -1 in shape

添加loss自适应的学习率衰减策略。

* raise index error when slice out of range; test=develop

* add uni test; test=develop

* fix format error; test=develop

* add comment for py::index_error; test=develop

* polish error message; test=develop

* polish error message; test=develop

* add clean up; test=develop

* add import; test=develop

PR types: Bug fixes
PR changes:Ops
Describe:
Fix the broadcast bug in elementwise ops, when elementwise ops do not have fast gradient calculate way，use the default way to calculate.

* Update sigmoid output from Y to out, test=develop (#24765)

* Collecting concat output threshold, test=develop (#24742)

* Add output threshold for ops that have several output activations, test=develop (#24726)

* [Fix bug] Init scale node in OutScaleForTrainingPass and enable test_quantization_scale_pass UT (#24393)

* Init scale node in OutScaleForTrainingPass, test=develop
* Enable test_quantization_scale, test=develop

Enhance error message of checkpoint_notify_op, fake_init_op gen_nccl_id_op and listen_and_serv_op (#24554) (#24844)

test=develop

* remove pow in speed up in dequantize_log test=develop

* remove pow in speed up in dequantize_log test=develop

* fix unittest test=develop

API/OP（sequence_first_step，sequence_last_step，sequence_mask，beam_search，beam_search_decode） error message enhancement ,test=release/1.8 (#24668)

* fix bug of varbase.__getitem__, test=develop (#24642)

* fix bug of varbase.__getitem__, test=develop

* fix bug of float and other type, test=develop

* fix unittest, 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)

* API(dynamic_gru, chunk_eval, BeamSearchDecoder) error message enhancement (#24513)

* dynamic_gru err_msg enhancement, test=develop

* chunk_eval err_msg enhancement and fix crf_decoding output type, test=develop

* BeamSearchDecoder err msg enhancement, test=develop

* API/OP(sequence_expand_as) error message enhancement (#23712) 
Co-authored-by: NGuo Sheng <whucsgs@163.com>

* fix convert call globals_funcs test=develop

* add import statement test=develop

* improve error reporting messages

* fix error check of stack and space_to_depth
* 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>

Enhance error message of cross_entropy_op, sigmoid_cross_entropy_with_logits_op, test=release/1.8 (#24542)

* Format error message for ops, test=release/1.8

* Fix check in sequence_expand, test=release/1.8

* fix error message, test=develop

* update err msg for dynamic_lstm and dynamic_lstmp, test=develop

test=release/1.8

l1_norm
norm
squared_l2_norm
squared_l2_distance
conv_shift
sample_logits

test=develop

* API/OP (Some SL API) error message enhancement  (#24441)

* polish some sl api error message, test=develop

* polish python input check of stride slice, test=develop

* fix unittest bugs, test=develop

* fix error info for transpose sequence_conv_pool max_sequence_len sequ… (#24437)

* fix error info for transpose sequence_conv_pool max_sequence_len sequence_erase, test=develop

* fix error info for transpose sequence_conv_pool max_sequence_len sequence_erase, test=develop

* update modify, test=develop

* update modify, test=develop

* fixed some modifications, test=develop
Co-authored-by: NXing Wu <wuxing03@baidu.com>

* remove print statement to make code clean(#23907)
* Try to fix UT Random Fail (#24223)

* add enable_imperative, disable_imperative; test=develop

* add unitest; test=develop

* polish example; test=develop