Attach (recommended) or Link to PDF file here:
[Testfile v1.5 to PDFA2.pdf](https://github.com/mozilla/pdf.js/files/6310752/Testfile.v1.5.to.PDFA2.pdf)


Configuration:
- Web browser and its version: Version 89.0.4389.114 (Offizieller Build) (x86_64)
- Operating system and its version: Windows 10 / MacOS BigSur
- PDF.js version: 2.5.207
- Is a browser extension: no 

Steps to reproduce the problem:
1.  Open Testfile v1.5 to PDFA2.pdf in pdf.js viewer demo
2. text is covered up by markings / highlights which are stored in pdf itself

What is the expected behavior? (add screenshot)
Should be displayed as in Acrobat Reader
<img width="1169" alt="Bildschirmfoto 2021-04-14 um 14 24 41" src="https://user-images.githubusercontent.com/1286150/114710202-bf175a80-9d2d-11eb-8d54-75481fe91b7d.png">

What went wrong? (add screenshot)
It's how it is displayed in pdf.js viewer
<img width="782" alt="Bildschirmfoto 2021-04-14 um 14 24 16" src="https://user-images.githubusercontent.com/1286150/114710311-d8200b80-9d2d-11eb-8000-b67b94488929.png">

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

fillColor,
        pointsCallback: (buffer, points) => {
          const x0 = points[0].x + this.borderStyle.width / 2;
          const y0 = points[0].y - this.borderStyle.width / 2;
          const x1 = points[3].x - this.borderStyle.width / 2;
          const y1 = points[3].y + this.borderStyle.width / 2;
          const xMid = x0 + (x1 - x0) / 2;
          const yMid = y0 + (y1 - y0) / 2;
          const xOffset = ((x1 - x0) / 2) * controlPointsDistance;
          const yOffset = ((y1 - y0) / 2) * controlPointsDistance;
          buffer.push(
            `${xMid} ${y1} m`,
            `${xMid + xOffset} ${y1} ${x1} ${yMid + yOffset} ${x1} ${yMid} c`,
            `${x1} ${yMid - yOffset} ${xMid + xOffset} ${y0} ${xMid} ${y0} c`,
            `${xMid - xOffset} ${y0} ${x0} ${yMid - yOffset} ${x0} ${yMid} c`,
            `${x0} ${yMid + yOffset} ${xMid - xOffset} ${y1} ${xMid} ${y1} c`,
            "h"
          );
          if (fillColor) {
            buffer.push("B");
          } else {
            buffer.push("S");
          }
          return [points[0].x, points[1].x, points[3].y, points[1].y];
        },
      });
    }
  }
}
class PolylineAnnotation extends MarkupAnnotation {