* add static_only for static api

* addd static_only for class init

* remove static_only for default_main_program

* remove creater_parameter & startup_program

* remove failed apis

* revert py_func import

* remove global scope

* remove some api

* remove cuda pinned place

* fix examples, test=document_fix

* fix, test=document_fix

add API serialize_program, serialize_persistables, save_to_file, deserialize_program, deserialize_persistables, load_from_file. (#29034)

* remove BatchSampler type check. test=develop

* add hapi api flops

* fix bug

* fix some bug

* add unit test

* fix unit test

* solve ci coverage

* fix doc

* fix doc

* fix static flops

* delete the comment

* fix some grammar problem in doc

* fix some bug

* fix some doc

* fix some doc

* Add bf16 pool2d and unify bf16 unit tests

* Add change default ops test

* Fix cpu_bfloat16_pass

* Add output_format

* Fix incorrect SetOutput

* Change fromating

* fix win ci failure, test=develop

* add ci test, test=develop

* default not show cpp statck & add hint

* fix failed unittest

* fix failed unittests

* Fix doc format for callbacks, metrics and Model
* Fix code sample and doc

* change load dict file one by one to warn

* add unittests for coverage

* polish error message

* fix cond error

* Rename variables when use 'jit.load'

* Check whether the original graph contains the variable with the same name

* add comment

* rename output/input of op and edit unittest

* modify the code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* fix syncbn

* add unittest

add uint8 for reshape operator

* rewrite the sigmoid_focal_loss code example. test=develop

* fix spelling mistake in comments of code example.test=develop

* change print([.*].numpy()) to print([.*]) in example codes of sigmoid_focal_loss. test=document_fix

* Support pop for dict in dy2stat

* Move convert_pop to convert_operators.py and polish convert_pop

* fix tensor detach to zero copy

* fix tensor detach to zero copy

* add reminder of fluid.layers.lstm

* save one name in cross_entropy and softmax_cross_entropy, test=develop

* change used function in CrossEntropy from softmax_cross_entropy to cross_entropy, test=develop

Simple code clean up

test=document_fix

* Impelement 2.0 API version Conv2d and Linear layer quantization in imperative mode.

* use cudnn softmax in static Lenet

* Modified ChannelwiseQAT Unittest for 2.0 API.

* For CI python coverage.

remove eigen threadpool for the speed up

* Add multi_gru_fuse_pass and tests

* fix date

* cleaned up headers

* polish parallel api impl & doc details

* add unittest for coverage

* remove spawn test in py2.7

* add parallel api into white list