cherry-pick from the develop PR#26792, fix the argmin, argmax

test=develop

update doc of paddle.to_tensor

* fix heter-ps multi thread

* update optimizer (#26711)

* update doc

* update doc

* fix optimizer sample code

* add default value for adamw weight_decay

* fix adamw

* change LearningRateDecay to _LRScheduler

* fix adamw;notest

* fix load;notest

* remove file

* bug fix

* fix code style

* bug fix

* add ut

* adamw support weight_decay=0

* fix ut

* fix set_lr doc

* fix doc

* change parameters place

* fix sample code

* add summary api

* refine paddle.stack

* support TensorArray

* add test

* fix coverage problem

* fix coverage problem

* fix sample code

Fix some code samples in Tranoformer apis.
test=develop

* fix dropout bug in backward when input is 1d tensor, test=develop

* add test case and refine error message, test=develop

* refine error message, test=develop

* set_default_type only take effect on python floats or complex

* fix doc

* fix norm bug, test=develop

* fix norm bug, test=develop

* fix norm bug, test=develop

* fix norm bug, test=develop

* fix norm bug, test=develop

* replace fluid.optimizer.set_dict with optimizer.set_state_dict

* replace fluid.optimizer.set_dict with optimizer.set_state_dict

* add coverage rate

* Increase coverage rate, fix code style

* Increase coverage rate, fix code style

* add fit to generate optimizer.state_dict() to save .pdopt to increase coverage rate

* delete http.log

* fix sample codes, test=develop

* fix fluid.embedding

* add embedding 2.0

* add embedding support input int32

* add check for bernoulli and register bool for unsqueeze

* follow comments

* remove backend argument of init_parallel_env

* remove keep name table in transformer

* add cpu version check

* add skip unittest for init_parallel_env

* polish doc: remove func use & update example

* add FleetAPI doc
Co-authored-by: Nliuyuhui <liuyuhui@baidu.com>

rename Dropout2D/3D to Dropout2d/3d

* refine cudnn softmax

* get use of global 'use_mkldnn' in layer_helper

* update for CI

* update for CI, relu test

* update for CI, relu test added, make FLAGS_use_mkldnn a public flag

* added more strict tests, fixes after review

* fixes after review

* fixes after review, CI stuff

* Fix Python Version compatibility

* add import six

fix doc, use to_tensor for the loss ops

* Move hapi form paddle/incubate to paddle

* Remove vision/datasets/utils.py and clean code

* Add sample code for conll05

* Print pull path when saving model

* Fix sample code after paramter_list of SGD is changed to parameters

* Fix bug in wmt16 datase