* fix warpctc dynamic library not found issue on mac and windows platform

* fix backward bug

* test=release/1.5, cherry-pick hide not_support for dygraph

* test=release/1.5, cherry-pick hide not_support for dygraph

Add path to handle 1D vector

test=release/1.5

* test=develop

* test=develop

* fix mac ci random fail
* use platform instead

test=release/1.5

replace mnist dataset url

* fix py-cpuinfo mac random fail
* differentiate version on windows

test=release/1.5

test=release/1.5

* Update lamb optimizer (#18333)

* Update lamb optimizer

* Regenerate api spec

test=release/1.5

* Give an experimental warning

test=release/1.5

* Simplify multi_box_head API in detection.py and remove assign op.

BackwardStrategy
dygraph.nn
dygraph.checkpoint

*  add cuda_is_available
test=release/1.5

* update pe reduce config
test=release/1.5

*  drop the local_exe_scopes of the previous parallel_executor
test=release/1.5

Socket can't be pickled.

test=release/1.5

* test=release/1.5, add mutigpu install check

* test=develop, refine code to use cuda_devices

* sequnce mask support max length tensor input; test=develop

* add rnn_impl.py; test=develop

* add basic gru lstm unittest; test=develop

* fix api spec; test=develop

* fix sequence_mask op bug;
test=develop
test=document_preview

* change +-*x to elmentwise_op; test=develop

* add mkl flag; test=develop

* fix rnn impl bug; test=develop

* update api spec; test=develop

* fix doc bug; test=develop

* fix lstm bugs; test=develop

test=release/1.5

* Fix the GetExpectedKernelType of add_position_encoding_op.

* Fix the doc of lstm_unit outputs in nn.py.

test=release/1.5

* fix paddle cloud role maker bug

* Revert "Cherry pick install check for multi gpu (#18245)"

This reverts commit d0219002.

* test=release/1.5, ci start

* fix default value of fluid.memory_optimize
test=release/1.5

cherry-pick for #18293

add dygraph api doc for fluidDoc and api spec

* fix slice op bug; test=develop

* fix variabel test bug; test=develop

* remove slice while true; test=develop

test=release/1.5

* refine core cmake warning and print more info
* fix comments

test=release/1.5

* test=develop, add add_multi_gpu_install_check (#18157)

* test=develop, add add_multi_gpu_install_check

* test=develop, refine warning doc

* test=develop, refine warning doc

* test=develop, refine warning doc

* test=develop, support multi cpu

* test=release/1.5, cherry-picked from develop

* update some op doc, test=release/1.5

* fix relative import error in python3
* fix debug string info

* fix_create_lod_tensor, test=release/1.5

* remove program_guard import,test=release/1.5

* fix windows numpy default int32 error, test=release/1.5

* Update backward appending stragety to support double backward and fix some bug. (#18104)

* Update backward.py:
     - If there is no input grad var in all outputs of previous ops, do not append this op into graph.
     - Only apply this stragety when double backward.
* Update some double backward op.
* Update sum_op to judge whether a tensor is empty by numel or IsInitialized().