* add helper function to get appropriate DeviceContext

* add KernelTypeToString interface

* cache memory in local scope

* fix typo

* refine trans logic

* add memory switch mechanism in operator kernel switch

* init data_transform

* complete DataTransform

* fix build error

* add data_transform_test

* add a register test for data_transform_fn

* use function to simulate registration macro

* add register macro

* update test

* clean code

* restore unrelated code

* update data transform test

* generate unique name for REGISTER_DATA_TRANSFORM_FN

* add const

* follow comment

* update KernelTypePair hash function