* Integrate accelerator abstraction interface into deepspeed/

* Fix error message in fp16/fused_optimizer

* fix error message in fp16/unfused_optimizer.py

* assign get_accelerator().pin_memory() result to input Tensor name

* no need to check cuda and whether nvtx supported

* move try-except into inner most block

* call Event() and Stream() in get_accelerator() for data type

* Make Stream and Event as properties of abstract interface so they can be used as data type in deepspeed

* Apply op_builder backend api change from #2705 from @jeffra

* fix tests where Builder NAME is used

* keep original ...Builder.NAME interface instead of ...Builder().NAME interface

* fix builder closure for installation

* fix randomltd builder

* add comments to clarify create_op_builder and get_op_builder

* fix compatibility with pip install -e
Co-authored-by: NCheng Li <pistasable@gmail.com>
Co-authored-by: NOlatunji Ruwase <olruwase@microsoft.com>