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["Calibri-Italic"] = "Helvetica-Oblique";
  t.CenturyGothic = "Helvetica";
  t["CenturyGothic-Bold"] = "Helvetica-Bold";
  t["CenturyGothic-BoldItalic"] = "Helvetica-BoldOblique";
  t["CenturyGothic-Italic"] = "Helvetica-Oblique";
  t.ComicSansMS = "Comic Sans MS";
  t["ComicSansMS-Bold"] = "Comic Sans MS-Bold";
  t["ComicSansMS-BoldItalic"] = "Comic Sans MS-BoldItalic";
  t["ComicSansMS-Italic"] = "Comic Sans MS-Italic";
  t["ItcSymbol-Bold"] = "Helvetica-Bold";
  t["ItcSymbol-BoldItalic"] = "Helvetica-BoldOblique";
  t["ItcSymbol-Book"] = "Helvetica";
  t["ItcSymbol-BookItalic"] = "Helvetica-Oblique";
  t["ItcSymbol-Medium"] = "Helvetica";
  t["ItcSymbol-MediumItalic"] = "Helvetica-Oblique";
  t.LucidaConsole = "Courier";
  t["LucidaConsole-Bold"] = "Courier-Bold";
  t["LucidaConsole-BoldItalic"] = "Courier-BoldOblique";
  t["LucidaConsole-Italic"] = "Courier-Oblique";
  t["LucidaSans-Demi"] = "Helvetica-Bold";
  t["MS-Gothic"] = "MS Gothic";
  t["MS-Gothic-Bold"] = "MS Gothic-Bold";
  t["MS-Gothic-BoldItalic"] = "MS Gothic-BoldItalic";
  t["MS-Gothic-Italic"] = "MS Gothic-Italic";
  t["MS-Mincho"] = "MS Mincho";
  t["MS-Mincho-Bold"] = "MS Mincho-Bold";
  t["MS-Mincho-BoldItalic"] = "MS Mincho-BoldItalic";
  t["MS-Mincho-Italic"] = "MS Mincho-Italic";
  t["MS-PGothic"] = "MS PGothic";
  t["MS-PGothic-Bold"] = "MS PGothic-Bold";