test=develop

* refine example code in en doc, test=develop, test=document_fix

* update shape to make it meaningful, test=develop, test=document_fix

* add instance_norm op for dygraph, test=develop

* add error message, test=develop

* add LayerList insert and extend
test=develop

* add index range check
test=develop

* add sample codes
test=develop

* refine sample code
test=develop

* API(to_variable/save_dygraph) error message enhancement

error message enhancement for py_func op. 

* Involves AfsAPI to resolve slow downloading.
* Mainly used in PaddleBox

* error message enhancement for Conv2DTranspose, test=develop

* fix error_message, test=develop

* solve the conflict of ops with the same name. test=develop

* error message of NCE API enhancement

Fix the bug of matmul test_case

* fix no_grad signature
test=develop

* check func name instead of doc
test=develop

* API(program_guard) error message enhancement test=develop

* fix Cycle import test=develop

* polish code according comment test=develop

* Layer add training attr, add Dropout Layer

* add unit test for Dropout
test=develop

* minor fix
test=develop

* add missing args
test=develop

* support global flag in dropout, add docs
test=develop

* minor fix
test=develop

* minor fix
test=develop

* refine code comments
test=develop

* refine Dropout
test=develop

* fix ut
test=develop

* arg expansion
test=develop

* sample code update
test=develop

* prop -> p
test=develop

* fix ut
test=develop

* minor check fix
test=develop

API/OP (ConditionalBlock) error message enhancement (#23480)

* Remove the NGraph engine from PDPD repository
1. Each operator was removed from the operator's directory
2. Each test was removed from the unittest directory
3. The parallel executor support was removed from the PDPD
4. The CMake file was removed from the PDPD
5. The NG flags were removed from the repository
test=develop

* Remove ngraph from:
1. Cmake file
2. Python file
test=develop

* API(fluid.gridents) error message enhancement test=develop

* fix unitest failed test=develop