Always emit asteriskToken and yield if parsed

[rbuckton]

Even though we don't yet support generator functions and methods, we do parse them. However, we do not emit the asterisk token or yield expression on output, which means that if I'm using --target ES6 my input does not align with my output for something we actually parse:

// a.ts
class C {
  *[Symbol.iterator]() {
    let a = yield 1;
  }
}

// a.js
class C {
  [Symbol.iterator]() {
    let a = ;
  }
}

We should just emit these tokens.