Enhance front-end to add op (#19433)

Enhance front-end to add op (#19433)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19433

For operator benchmark project, we need to cover a lot of operators, so the interface for adding operators needs to be very clean and simple. This diff is implementing a new interface to add op.

Here is the logic to add new operator to the benchmark:
```
long_config = {}
short_config = {}

map_func

add_test(
  [long_config, short_config],
  map_func,
  [caffe2 op]
  [pt op]
)
```

Reviewed By: zheng-xq

Differential Revision: D14791191

fbshipit-source-id: ac6738507cf1b9d6013dc8e546a2022a9b177f05