* standard api

* fix xpu bugs

* remove using lodtensor part1

* polish history code format

* remove cudaDeviceContext

* remove more template

* fix rocm compile

* remove alias name CUDADeviceContext

* fix compile

* fix tests

* revert changes

* refactor the optional tensor

* remove optiona<MetaTensor> in InferMeta

* fix bug

* fix optional<vector<Tensor>>

* fix bug

* fix rmsprop

* fix amp of eager_gen

* polish code

* fix deleted code

* fix merge conflict

* polish code

* remove is_nullopt_

* fix merge conflict

* fix merge conflict

* update

* fix bugs; test=develop

* update; test=develop

* fix test compile error; test=develop

* fix cpu compile error; test=develop

* fix test error; test=develo

* fix layer_norm_op plugin error; test=develop

* fix error; test=develop

* fix test bug; test=develop

* update; test=develop

* polish code; test=develop

* fix bugs; test=develop

* remove unused depency; test=develop

* polish code; test=develop

* move dropout to phi; test=develop

* fix xpu, npu compile error; test=develop

* rename pten dir to phi

* rename namespace to phi

* rename infrt pten dir to phi

* resolve conflict

* rename pten to phi in cmake

* revert all infrt change

* change needed files

* fix infrt failed

* fix inference failed

* move operators/math/math_function_* to pten/kernels/func
* namespace from `paddle::operators::math` to `pten::funcs`

Fused elementwise_add, dropout, elementwise_add and layer_norm into one operator, only support Forward. 
No Python API changed.