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
```
constructor(parameters) {
    super(parameters);
    this.data.annotationType = AnnotationType.UNDERLINE;
    const quadPoints = (this.data.quadPoints = getQuadPoints(
      parameters.dict,
      null
    ));
    if (quadPoints) {
      if (!this.appearance) {
        /
        const strokeColor = this.color
          ? Array.from(this.color).map(c => c / 255)
          : [0, 0, 0];
        const strokeAlpha = parameters.dict.get("CA");
        this._setDefaultAppearance({
          xref: parameters.xref,
          extra: "[] 0 d 1 w",