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.contentVisible) {
        return;
      }
      this.groupLevel--;
      const groupCtx = this.ctx;
      this.ctx = this.groupStack.pop();
      
      
      if (this.ctx.imageSmoothingEnabled !== undefined) {
        this.ctx.imageSmoothingEnabled = false;
      } else {
        this.ctx.mozImageSmoothingEnabled = false;
      }
      if (group.smask) {
        this.tempSMask = this.smaskStack.pop();
      } else {
        this.ctx.drawImage(groupCtx.canvas, 0, 0);
      }
      this.restore();
    }
    beginAnnotations() {