* execute use kernel_key first

* change OpKernelType->KernelKey

* fix py3 compile error, remove redundant header files

* fix build_strategy_test

* fix DataType::RAW

* fix custom_type test: operator_test.cc

* fix transform place

* fix backends_are_same_class

* try fix place TransDataDevice

* support all KernelKey

* fix TransformData

* fix place_are_same_class

* fix merge

* fix test_params_no_grad

* fix specific place of GetExpectedKernelType

* fix specific place of GetExpectedKernelType

* fix GetKernelTypeForVar

* fix dtype error

* fix fetch_v2

* change GetKernelTypeForVar

* fix interpreter

* fix typo error

* polish codes

* polish codes

* polish codes

* fix conflict