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.

t["MS-PGothic-BoldItalic"] = "MS PGothic-BoldItalic";
  t["MS-PGothic-Italic"] = "MS PGothic-Italic";
  t["MS-PMincho"] = "MS PMincho";
  t["MS-PMincho-Bold"] = "MS PMincho-Bold";
  t["MS-PMincho-BoldItalic"] = "MS PMincho-BoldItalic";
  t["MS-PMincho-Italic"] = "MS PMincho-Italic";
  t.NuptialScript = "Times-Italic";
  t.SegoeUISymbol = "Helvetica";
  t.Wingdings = "ZapfDingbats";
  t["Wingdings-Regular"] = "ZapfDingbats";
});
const getSerifFonts = getLookupTableFactory(function (t) {
  t["Adobe Jenson"] = true;
  t["Adobe Text"] = true;
  t.Albertus = true;
  t.Aldus = true;
  t.Alexandria = true;
  t.Algerian = true;
  t["American Typewriter"] = true;
  t.Antiqua = true;
  t.Apex = true;
  t.Arno = true;
  t.Aster = true;
  t.Aurora = true;
  t.Baskerville = true;
  t.Bell = true;
  t.Bembo = true;
  t["Bembo Schoolbook"] = true;
  t.Benguiat = true;
  t["Berkeley Old Style"] = true;