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
```
const canvasAndCtx = CanvasFactory.create(
        viewport.width,
        viewport.height
      );
      const renderTask1 = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
        optionalContentConfigPromise,
      });
      const renderTask2 = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
        optionalContentConfigPromise,
      });
      await Promise.all([
        renderTask1.promise,
        renderTask2.promise.then(
          () => {
            
            expect(false).toEqual(true);
          },
          reason => {
            
            expect(/multiple render\(\)/.test(reason.message)).toEqual(true);
          }
        ),
      ]);
    });