Generate benchmarks automatically (#5561)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5561

## Context

Use the automatic test generation infrastructure to generate operator benchmarks. The overall concept is the same as the test generation; we just structure the generated code in the style of the google benchmark library instead of GTEST.
ghstack-source-id: 244287193

Reviewed By: derekxu, nathanaelsee

Differential Revision: D63286132

fbshipit-source-id: 25c379accf6664dfca8232db81772b638b41c758