[WIP] Add support for class member variable

I've submitted this PR as WIP to get feedback, **the code does not work for now**

I am looking for:
- feedback on the implemenation,
- how to debug (currently I'm doing make + node debug which is not the most user friendly workflow),
- what kind of test should be added.

/cc @arv
This is not the right place to put this. It is better to do this after the class declaration/class expression. But that will not work since we are never setting that property.

Maybe skip static in this PR.