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 (!annotationStorage) {
      return null;
    }
    const storageEntry = annotationStorage.get(this.data.id);
    const value = storageEntry && storageEntry.value;
    if (value === this.data.fieldValue || value === undefined) {
      return null;
    }
    let appearance = await this._getAppearance(
      evaluator,
      task,
      annotationStorage
    );
    if (appearance === null) {
      return null;