* Support python3.8

test=notest

* pass compatibility

* add compatibility registry

* add unittests for different padding

* add assert

* drop errmsg

* rm dependence of cv2

* fix cudnn dyload error

https://github.com/PaddlePaddle/Paddle/pull/27332

* 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

* fix op print error info problem. test=develop

* fix build error

* fix format

* fix error msg info

* fix format

and optimize the c++ implmentation of empty op as PR#26659 reviews,
and add bool for shape op.

* test=develop, util documents

paddle/fluid/operators/distributed_ops OP报错信息优化

* Fix install pr requirements.txt

* test=document_fix

Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOS with python>=3.8 (#27317)

* Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOs when python>=3.8

test=develop

enhance reduce op which can reduce tensor with arbitrary rank 

* update model.save_inference_model

* update doc for _save_inference_model, delete useless class in unittests

* make users not be able to set model._inputs be None

* update usage of Model class in unittests

* fix bugs of _verify_spec

* fix bugs of _verify_spec

* add unittest to increase coverage rate

* delete http.log

* update doc for save, remove requirments and limitations for using

* update doc for class Model

* fix floordiv

* Refine the unittest to support py38

    test=develop

Change ProgramTranslator.enable_declarative to ProgramTranslator.enable_to_static to meet API 2.0

* fix fleet dynamic-mode en-doc;test=develop

* add op_function_generator.exe retry in windows, test=develop

* modify test_imperative_using_non_zero_gpu from use two gpus to one gpu, test=develop

* remove objgraph

* remove graphviz

* fix ut

* add adaptivelsgd

* Todo fix the code to avoid the conflict.

Error description optimize for the math dir