Merge pull request !4845 from zhangxinfeng3/master

fix ci

Merge pull request !4706 from Peilin/smoothL1Loss-fix

Merge pull request !4314 from nhussain/clean_up_bindings

Merge pull request !4683 from yoonlee666/cisplit

Merge pull request !4843 from xychow/remove-ccsrc-common-h

Merge pull request !4847 from xiefangqi/xfq_add_numworker_validate

Merge pull request !4688 from amongo/FixBoolParse

Merge pull request !4758 from VectorSL/nhwc-support

replace frontend/operator/ops.h in backend with base/core_ops.h as
backend should not use any frontend-only primitive

Merge pull request !4831 from byweng/add_test

add testcase of st

Merge pull request !4754 from hexia/add_http_to_st_serving

Merge pull request !4744 from lichen/support_bert

Merge pull request !4796 from xiefangqi/fix_randomdata_ut

Merge pull request !4782 from islam_amin/bbox_class

Merge pull request !4689 from zhangbuxue/add_check_for_user_define_bprop_in_Pynative_mode

fix pylint

changed doc and code for SmoothL1Loss to be same a dchip. fixed grad kernel

fix ci

implment pause in MapOp, added more to callback

add ds_callback

- Initial drop of Python DSCallback

- Pybind DSCallback

- Pybind DSCallback

added callback to mapOp

- de_pipeline DSCallback

- de_pipeline DSCallback

add test case, segfault for now

fix seg fault

- de_pipeline DSCallback

remove 1 line

update callback test case, now works

use builder class for mapOp callback

- de_pipeline DSCallback

- de_pipeline DSCallback

- de_pipeline DSCallback

better test case

minor fix

add comments and minor clean ups

get rid of nullptr in MapOp, use other flag instead

fix a bug ParseMapOp only takes 1 callback

- Added WaitedDSCalabck

refactor callback param

fix text case incorrect number

- added testing

fix cpp test case

- added testing

- revert back lenet changes

- cleanup test_callbacks.py

- cleanup test_callbacks.py

fix CI stage I

fix CI stage II

fix CI and update epoch counter

- add validation
- add more testing  test_callbacks.py

use random data op to do tests

adjust when to call EpochBegin/End

- add repeat with callback

- addressing reviewers' comments

- docstring and CI fixes

- docstring and CI fixes

- docstring and CI fixes

- rebase with upstream/master

fix cpp test case

fix review comments

addr review cmts, add test case

Merge pull request !4685 from ZPaC/master-supports-export-server-ckpt

Merge pull request !4696 from jiangzhiwen/jzw/c_api_csv

Merge pull request !4722 from lijiaqi/modify_error_type

Merge pull request !4622 from hexia/http_init

Merge pull request !4498 from heleiwang/gnn_distributed

Merge pull request !4690 from baihuawei/categorical

Merge pull request !4723 from yangzhenzhang/concat-more-than-3-tensors

Merge pull request !4422 from xiefangqi/xfq_c++api_randomdata