* [Eager] Support eager grad interface, draft version

* Support eager grad interface with allow_unused and multi startup_op

* Fix code format

* Fix allow_unused case, return PyNone if tensor not initialize

* Support output's stop_gradient related to create_graph

* Support grad exception case in eager mode, fix coverage CI

* Update ToPyObject, return PyNone if not initialize

* AccumulationNode add FLAGS_retain_grad_for_all_tensor

* Fix ci issue

* Fix CI issue

* fix, use core.eager.Tensor

* Add func SetBufferSlotRankZeros for GradTensorHolder

* Support retain_graph by using ClearTensorWrappers

* Support retain_graph by using ClearTensorWrappers

* Update retain_graph and no_grad_vars related test case

* Update code gen logic for ClearTensorWrappers

* Fix by override statement

* fix override func args

* Support retain_graph, update unit tests

* Updated ClearTensorWrappers logic

* fix grad python interface

* Use deep copy and update unit tests

* Polish code

* Polish code

* Fix CI issue, Deep copy only use when user set grad_tensors

* Fix CI, use Backward instead RunBackward

* Fix CI, Declare kernel explicitly in test file

* Polish, remove vector of TensorWrapper

* Refactor the logic of grad/backward, polish codes

* Update code after merge upstream develop

* Polish after merge upstream develop

* Update to adapt new GradNodeBase superclass

* Fix error introduced during conflict resolution

* Update purify potential_startup_nodes logic

* Fix errors

* Polish code

* Remove useless args for ToPyObject

* Remove useless TensorWrappersSet

* Fix code-format, re-install pre-commit

* Fix pre-process logic for potential_startup_ops

* Update unit tests, use eager mode

* open eager when WITH_PYTHON, test=develop

* refine, test=develop

* refine, test=develop

* add DWITH_PYTHON for gen_fluid_lib, test=develop

* [Eager] Support GradientHook before running seperate GradNode

* Fix CI issue

* Fix CI issue

* Enabled performance benchmark tests for Eager Dygraph

* Protected CUDA tests with macro

* Fixed dependency issues for windows-ci

* Added GradTensorHolder to Eager Dygraph

* Added accumulation codes to Eager Dygraph

* Added tensor utils to Eager Dygraph

* Resolve compilation issues

* Fixed issues

* Added EagerUtils to Eager Dygraph

* Purified include dependencies for global_utils

* Fixed merge conflicts

* Add EagerTensor and tests

* remove useless enforce

* remove comment in cmake

* support autograd meta

* support grad node info test

* support grad_node_info

* add more edge test

* remove Python.h

* add tensor wrapper with tests

* support compute require grad and stop gradient

* support sync methods and global utils

* support pure cpu test

* refine error msg

* refine error msg

* refine error info

* fix npu error