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._objs = Object.create(null);
  }
}
/**
 * Allows controlling of the rendering tasks.
 */
class RenderTask {
  constructor(internalRenderTask) {
    this._internalRenderTask = internalRenderTask;
    /**
     * Callback for incremental rendering -- a function that will be called
     * each time the rendering is paused.  To continue rendering call the
     * function that is the first argument to the callback.
     * @type {function}
     */
    this.onContinue = null;
  }
  /**
   * Promise for rendering task completion.
   * @type {Promise<void>}
   */
  get promise() {
    return this._internalRenderTask.capability.promise;
  }
  /**
   * Cancels the rendering task. If the task is currently rendering it will
   * not be cancelled until graphics pauses with a timeout. The promise that
   * this object extends will be rejected when cancelled.
   */
  cancel() {