Move tracer impls into cpp file (#16410)
Summary:
Working on the tracer was really annoying because a lot of the implementations were in `tracer.h` and editing that file caused us to rebuild almost the whole world. So this moves all the implementations into tracer.cpp
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16410
Differential Revision: D13847776
Pulled By: jamesr66a
fbshipit-source-id: ec8500da32b2d4cd990f293a0a96101d3e82f158
