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
```
annotation.setContents("Foo bar baz"
      expect(annotation.contents).toEqual("Foo bar baz"
    }
    it("should not set and get invalid contents", function () {
      const annotation = new Annotation({ dict, ref }
      annotation.setContents(undefined
      expect(annotation.contents).toEqual(""
    }
    it("should set and get a valid modification date", function () {
      const annotation = new Annotation({ dict, ref }
      annotation.setModificationDate("D:20190422"
      expect(annotation.modificationDate).toEqual("D:20190422"
    }
    it("should not set and get an invalid modification date", function () {
      const annotation = new Annotation({ dict, ref }
      annotation.setModificationDate(undefined
      expect(annotation.modificationDate).toEqual(null
    }
    it("should set and get flags", function () {
      const annotation = new Annotation({ dict, ref }
      annotation.setFlags(13
      expect(annotation.hasFlag(AnnotationFlag.INVISIBLE)).toEqual(true
      expect(annotation.hasFlag(AnnotationFlag.NOZOOM)).toEqual(true
      expect(annotation.hasFlag(AnnotationFlag.PRINT)).toEqual(true
      expect(annotation.hasFlag(AnnotationFlag.READONLY)).toEqual(false
      expect(annotation.hasFlag(AnnotationFlag.HIDDEN)).toEqual(false
    }
    it("should be viewable and not printable by default", function () {
      const annotation = new Annotation({ dict, ref }
      expect(annotation.viewable).toEqual(true