Add support for initializing member variables

The implementation follow TS rules:
- when the memberVariables option is enabled, the constructor must call the super constructor,
- when the memberVariables option is enabled and a class has initialized instance variables, the call to the super constructor must be the first statement in the class own constructor,
- instance variables initializers are evaluated when the class is instantiated.
We would need to skip the prolog to make it correct. Do we want to do that ?

```
constructor() {
  "use strict;"
  this.method();
}
```
the error should be reported on the second statement