Abstract accelerator (step 1) (#2504)
* Establish building block of abstract accelerator
* Change .*Tensor variable to @property
* [op builder] add op builder reflection to allow enumerate of builders in all_ops.py and builder_names.py
* change @abstractproperty to @property @abstractmethod
Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
