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["Bernhard Modern"] = true;
  t["Berthold City"] = true;
  t.Bodoni = true;
  t["Bauer Bodoni"] = true;
  t["Book Antiqua"] = true;
  t.Bookman = true;
  t["Bordeaux Roman"] = true;
  t["Californian FB"] = true;
  t.Calisto = true;
  t.Calvert = true;
  t.Capitals = true;
  t.Cambria = true;
  t.Cartier = true;
  t.Caslon = true;
  t.Catull = true;
  t.Centaur = true;
  t["Century Old Style"] = true;
  t["Century Schoolbook"] = true;
  t.Chaparral = true;
  t["Charis SIL"] = true;
  t.Cheltenham = true;
  t["Cholla Slab"] = true;
  t.Clarendon = true;
  t.Clearface = true;
  t.Cochin = true;
  t.Colonna = true;
  t["Computer Modern"] = true;
  t["Concrete Roman"] = true;
  t.Constantia = true;
  t["Cooper Black"] = true;