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):

pageIndex,
    };
    switch (subtype) {
      case "Link":
        return new LinkAnnotation(parameters);
      case "Text":
        return new TextAnnotation(parameters);
      case "Widget":
        let fieldType = getInheritableProperty({ dict, key: "FT" });
        fieldType = isName(fieldType) ? fieldType.name : null;
        switch (fieldType) {
          case "Tx":
            return new TextWidgetAnnotation(parameters);
          case "Btn":
            return new ButtonWidgetAnnotation(parameters);
          case "Ch":
            return new ChoiceWidgetAnnotation(parameters);
          case "Sig":
            return new SignatureWidgetAnnotation(parameters);
        }
        warn(
          `Unimplemented widget field type "${fieldType}", ` +
            "falling back to base field type."
        );
        return new WidgetAnnotation(parameters);
      case "Popup":
        return new PopupAnnotation(parameters);
      case "FreeText":
        return new FreeTextAnnotation(parameters);
      case "Line":