Enable newer JavaScript syntax

[onsetsu]

Currently, we are a bit behind the browser implementations, which seems wrong to me.

E.g. the following code can be parsed and executed in Blink DevTools but not in a workspace.

class Timer2 {
  start = Date.now();
  current = Date.now();

  tick() {
    this.current = Date.now();
  }
}

I think we should come up with some future-prove solution here: How to do this knowing never syntax extensions wont stop coming?