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
```
this.gfx.beginDrawing({
        transform,
        viewport,
        transparency,
        background,
      });
      this.operatorListIdx = 0;
      this.graphicsReady = true;
      if (this.graphicsReadyCallback) {
        this.graphicsReadyCallback();
      }
    }
    cancel(error = null) {
      this.running = false;
      this.cancelled = true;
      if (this.gfx) {
        this.gfx.endDrawing();
      }
      if (this._canvas) {
        canvasInRendering.delete(this._canvas);
      }
      this.callback(
        error ||
          new RenderingCancelledException(
            `Rendering cancelled, page ${this._pageIndex + 1}`,
            "canvas"
          )
      );
    }
    operatorListChanged() {