Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

const renderer = FontRendererFactory.create(this, SEAC_ANALYSIS_ENABLED);
    return shadow(this, "renderer", renderer);
  }
  exportData(extraProperties = false) {
    const exportDataProperties = extraProperties
      ? [...EXPORT_DATA_PROPERTIES, ...EXPORT_DATA_EXTRA_PROPERTIES]
      : EXPORT_DATA_PROPERTIES;
    const data = Object.create(null);
    let property, value;
    for (property of exportDataProperties) {
      value = this[property];
      
      if (value !== undefined) {
        data[property] = value;
      }
    }
    return data;
  }
  fallbackToSystemFont(properties) {