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 POINT_TO_PROCESS_LIMIT = 1000;
  const POINT_TYPES = new Uint8Array([
    0, 2, 4, 0, 1, 0, 5, 4, 8, 10, 0, 8, 0, 2, 1, 0,
  ]);
  const width = imgData.width,
    height = imgData.height,
    width1 = width + 1;
  let i, ii, j, j0;
  const points = new Uint8Array(width1 * (height + 1));
  
  const lineSize = (width + 7) & ~7,
    data0 = imgData.data;
  const data = new Uint8Array(lineSize * height);
  let pos = 0;
  for (i = 0, ii = data0.length; i < ii; i++) {
    const elem = data0[i];
    let mask = 128;
    while (mask > 0) {
      data[pos++] = elem & mask ? 0 : 255;
      mask >>= 1;
    }
  }