Further Module improvements. (#1622)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1622

- Merge Runner and Module
- Init runtime in constructor
- Allow injecting event tracer
- Allow providing verification mode at load
- Utilize check and unwrap macros for brevity

Reviewed By: dbort

Differential Revision: D52846711

fbshipit-source-id: fc02beb18ddf7740f6329b093e7704a3a4e353aa