Configuration:
- PDF.js version: 2.0.550

Steps to reproduce the problem:
1. Render document in SVG mode `renderMode="svg"`

What is the expected behavior? (add screenshot)
Rendering annotations same way as they rendered on canvas

What went wrong? (add screenshot)
```
Warning: Unimplemented operator beginAnnotations
Warning: Unimplemented operator endAnnotations
```
if (!this.graphicsReady) {
        if (!this.graphicsReadyCallback) {
          this.graphicsReadyCallback = this._continueBound;
        }
        return;
      }
      if (this.stepper) {
        this.stepper.updateOperatorList(this.operatorList);
      }
      if (this.running) {
        return;
      }
      this._continue();
    }
    _continue() {
      this.running = true;
      if (this.cancelled) {
        return;
      }
      if (this.task.onContinue) {
        this.task.onContinue(this._scheduleNextBound);
      } else {
        this._scheduleNext();
      }
    }
    _scheduleNext() {