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):

return this.appearance.dict.getAsync("Resources").then(resources => {
      if (!resources) {
        return undefined;
      }
      const objectLoader = new ObjectLoader(resources, keys, resources.xref);
      return objectLoader.load().then(function () {
        return resources;
      });
    });
  }
  getOperatorList(evaluator, task, renderForms, annotationStorage) {
    if (!this.appearance) {
      return Promise.resolve(new OperatorList());
    }
    const appearance = this.appearance;
    const data = this.data;
    const appearanceDict = appearance.dict;
    const resourcesPromise = this.loadResources([
      "ExtGState",
      "ColorSpace",
      "Pattern",
      "Shading",
      "XObject",
      "Font",
    ]);
    const bbox = appearanceDict.getArray("BBox") || [0, 0, 1, 1];
    const matrix = appearanceDict.getArray("Matrix") || [1, 0, 0, 1, 0, 0];
    const transform = getTransformMatrix(data.rect, bbox, matrix);
    return resourcesPromise.then(resources => {
      const opList = new OperatorList();