* reimplement paddle.nn.functional.sigmoid_focal_loss. test=develop

* fix reduction error message. test=develop

* fix exp. test=develop

* reset the shape of logit. test=develop

* delete disable_static in example. test=develop

* keep summary mode unchange

* add no grad decorator

* fix bilateral bug

* modify doc for ParameterList and LayerList, test=develop

* add empty line after code-block, test=develop

* modify doc for Layer, test=develop

* modify doc for Layer2, test=develop

* set dtype default value to float32, test=develop

* add example code for paddle.nn.Layer, test=develop

* set create_parameter and create_variable dtype default value to None, test=develop

* modify some example code, tet=develop

* refine, test=develop

* del no ues code, test=develop

* modify doc, example code, args, test=develop

* modify doc, test=develop

* fix huber_loss ans npair_loss doc and example code, test=document_fix

* remove disable_static in example code, test=document_fix

* remove huber_loss and refine npair_loss example code, test=document_fix

* remove huber_loss in functional/__init__.py, test=document_fix

Add Simnet Test for V2 APIs.

We used tool from https://www.paddlepaddle.org.cn/documentation/docs/zh/2.0-beta/guides/migration_cn.html#paddle1-xpaddle2-0beta to do v1.x to v2 transformation.

This PR pulled changes from #27430, please DO NOT merge before #27430 is merged

* Add test skip from cmake

* Remove print

* Add avx instructions check

* Small fix

* Change function name

* Change uint to unsigned int

* Fix ErrorClipByValue api and demo code of clip_by_value. test=develop
Co-authored-by: Ntianshuo78520a <707759223@qq.com>

* test=develop, update example

* move dygraph amp api to paddle

* refine code and add unit test

* add visualdl callback

* add multinomial cpu kernel

* fix C++ notype error

* fix windows ci array len error

* let array len be const

* change array to vector

* add cuda kernrl with num_distribution is 1, and not support replacement=False

* add multinomial python api

* support num_distribution different multinomial distributions

* add categorical class

* fix test_distribution enable_static error

* add unittest for different setting of Categorical

* optimize format

* little change

* little change

* add raise error if shape not match, optimize format

* fix windows CI dtype error in concat

* little changes

* little changes2

* change values type to int64

* change values type to int64

* change values type to int64

* Add test_resnet_v2.py test=develop

* refine grid_sample and temporal_shift

* fleet support non_distributed training in dygraph mode; test=develop

* add double grad for expand, test=develop

* add xpu test

* notest;add kunlun_test

* notest;add kunlun_test

* notest;test=kunlun

* notest;test=kunlun

* notest;test=kunlun

* notest;test=kunlun

* test=kunlun

* remove input requirment in dygraph Model

* correct unittest

* upadte save inference model in dygraph without input

* fix unittets for test_model.py

* solve conflicts

* solve conflicts

* delete http.log

* fix test_model.py bug, correct initialization of MyModel

* fix unittests bugs

* set paddle manual seed for unittest

* fix Model bugs, because inputs can be list or dict when it is provided.

* add random seed for test_export_deploy_model

* delete redundant codes, because  calls

* Code optimization, error information optimization

* update 2.0 API for dice_loss and log_loss test=document_fix

* fix test_se_resnet unittest

* fix test_se_resnet unittest

* add comments for decresing test_se_resnet precision

* fix the scatternd/scatterndadd

* fix the doc of scatter

* replace rank with ndim

As the title

* migrate code example and doc