* save InferVarType changes, test=develop

* remove code comments, test=develop

* tweak code, test=develop

* fix compilation warning, update merge_ids_op split_ids_op to new interface, test=develop

* modify fused_bn_activation_op, test=develop

* fix error of fused_bn_activation_op, test=develop

* fix PADDLE_ENFORCE and unittest coverage issue, test=develop

* tweak PADDLE_ENFORCE messages, test=develop

* improve unittest coverage, test=develop

* add StaticGraphInferVarType class, test=develop

* rebase develop branch, test=develop

* fix unittest error, test=develop

* remove comments, test=develop

* improve unittest coverage, test=develop

* imporve error message and imporve unittest coverage, test=develop

* upgrade InferVarType API, test=develop

* tweak pyfunc error message, test=develop

* fix compilation conflict - save_combine_op, test=develop

* define fluid alias in paddle.tensor and paddle.nn dir test=develop

* from layer import loss in paddle.nn dir test=develop

* add to_readable_code method, test=develop

* polish doc details, test=develop

* polish doc note, test=develop

* fix unittest error, test=develop

* fix coverage, test=develop

* add print test, test=develop

* add print param, test=develop

* hidden to_readable_code api, test=develop

* remove original tool methods, test=develop

* remove old api using code, test=develop

python API(get_tensor_from_selected_rows and tensor_array_to_tensor)error message enhance, test=develop (#23636)

* adapt old version pretrain model load, test=develop

* fix infer error & multiple input error, test=develop

* update index sample

* add decorator, test=develop

* add fake_interface_only, test=develop

* remove some dygraph_not_support, test=develop

* change dygraph to imperative, test=develop

* add kron op and its python API, doc and unittests.
* add kron in paddle.complex

fix the bug in inferVartype in the uniform_random op, add the support the set of dtype 

This reverts commit 652e804b.
test=develop

* API/OP (affine_channel, group_norm, layer_norm, random_crop, unpool, log_loss) error message enhancement test=develop

* Add cholesky_op forward part. test=develop

* Complete cholesky_op forward part. test=develop

* Add cholesky_op backward part. test=develop

* Complete cholesky_op backward part. test=develop

* Refine cholesky_op error check and docs. test=develop

* Add grad_check unit test for cholesky_op. test=develop

* Fix sample code in cholesky doc. test=develop

* Refine some error messages of cholesky_op. test=develop

* Refine some error messages of cholesky_op. test=develop

* Remove unused input in cholesky_grad. test=develop

* Remove unused input in cholesky_grad. test=develop

* Fix stream for cusolverDnSetStream. test=develop

* Update PADDLE_ENFORCE_CUDA_SUCCESS from cholesky_op to adapt to latest code.
test=develop

* Add CUSOLVER ERROR in enforce.h
test=develop

* Fix the missing return value in cholesky. test=develop

* [Dy2Stat] Add test for ptb model. test=develop

* Simplify code for gast.If in is_control_flow_to_transform. test=develop

* Move IsControlFlowVisitor to file utils. test=develop

* Don't use convert_call for build-in func in CallTransformer. test=develop

* Optimize api is_control_flow_to_transform. test=develop

* Polish the document of IsControlFlowVisitor. test=develop

* Use declarative instead of dygraph_to_static_func. test=develop

* Add trainable_statistics in attr for batch_norm
* Unifying behavior of dynamic graph and static graph

* Simplify code for gast.If in is_control_flow_to_transform.
* Move IsControlFlowVisitor to file utils. 
* Don't use convert_call for build-in func in CallTransformer. 
* Optimize api is_control_flow_to_transform. 
* Polish the document of IsControlFlowVisitor.

test=develop

* Update creation.py

* change int to floor, test=develop

* fix unittest, test=develop

* Indent MSELoss example docs

* Point out input tensors should be of same shape

test=develop

* Document `MSELoss` input and return parameters

test=develop,test=document_fix