refactor fleet api under paddle.fleet
update DistributedStrategy

* add reinforcement learning model test=develop

* align backward test=develop

* add gym in paddle_build.sh test=develop

* rm pip install in script test=develop

* refine paddle_build.sh test=develop

* fix sed error in macOS test=develop

* polish code test=develop

* refine infer ir pass tests, test=develop

* commit to change copy_from_cpu input to np array, test=develop

Enable multiple "return" statement in MNIST as Unit test in dy2stat.

* fix test_activation_op, test=develop

* remove paddle.mul related unittest, test=develop

* delete mul op. test=develop,test=document_fix

* bug fix. test=develop,test=document_fix

Add Support for SelectedRows for Transpose OP and Fix a Bug That SelectedRows Cannot be Supported in SimNet (#25536)

This PR fixes a bug that SelectedRows cannot be supported in SimNet. The reason of this bug is that dygraph basic_engine didn't copy var's type when the var needs to be accumulated during backward. So when a var is SelectedRows and needs to be accumulated, like SimNet which calls net for two times, the var's type will be changed to default LoDTensor thus bug happens. To fix it, we just also copy the type.

Without this PR, the accumulated SelectedRows parameters in dygraph will be changed into LoDTensor. So when we fixed the bug of supporting SelectedRows in SimNet, we found `test_imperative_lod_tensor_to_selected_rows` failed and threw the error that SelectedRows was not supported for Transpose OP. To fix it, too, this PR also added support for SelectedRows for Transpose OP.

* remove op call stack test=develop

* fix typo test=develop

* fix paddle/fluid/framework/ir/ error msg reoprt, test=develop

* modify error msg reoprt in ir/, about errortype, grammar, supplementary infor, test=develop

* modified some unclear descriptions, test=develop

* Modify the problem that report msg is less than 20 characters, test=develop

* fix doc of logical_* op.

* fix doc of op pow.

* fix comment syntax error9D

* fix operator reciprocal demo.

* fix logical_* ops' doc. test=develop,test=document_fix

* bug fix. test=develop,test=document_fix

* bug fix. test=develop,test=document_fix

* bug fix. test=develop,test=document_fix

* bug fix. test=develop,test=document_fix

* fix topk_avg_pool hang test=develop

* refactor get_topk_pos test=develop

* add check of channel_num and num_k test=develop

* add TopKPosPaddingId test=develop

add try..catch...

* add bilateral slice op

* Refine PADDLE_ENFORCE in paddle/fluid/platform
test=develop

* fix paddle/fluid/framework/ir/mkldnn/ error msg reoprt, test=develop

* modify error msg reoprt, about errortype, grammar, supplementary infor, test=develop

* modified some error descriptions, test=develop

* fix paddle/fluid/framework/ir/multi_devices_graph_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/memory_optimize_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/fuse_optimizer_ops_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/memory_optimize_pass/ error msg reoprt about PADDLE_ENFORCE, test=develop

* modify error msg reoprt,about errortype，grammar. test=develop

* modify error msg reoprt,about PADDLE_ENFORCE to PADDLE_ENFORCE_XXX, test=develop

* modify error msg reoprt,about PADDLE_ENFORCE to PADDLE_ENFORCE_XXX, and %s to %d, test=develop

* modified some error descriptions, test=develop

* randint API: remove out, devive, stop_gradient; add name; test=develop

* test=develop

* test=develop

* test=develop

According to paddle 2.0 standard
1, change flip api attr name 'dim' to 'axis'.
2, support empty axis
3, change example code to imperative mode.

According to paddle 2.0 standard.
1, chang api to def meshgrid(*args, **kwargs) we hide name argument in **kwargs.
2, add relate ut.
3, change example code to imperative mode