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.

if (
      !glyph ||
      !glyph.matchesForCache(
        charcode,
        fontChar,
        unicode,
        accent,
        width,
        vmetric,
        operatorListId,
        isSpace,
        isInFont
      )
    ) {
      glyph = new Glyph(
        charcode,
        fontChar,
        unicode,
        accent,
        width,
        vmetric,
        operatorListId,
        isSpace,
        isInFont
      );
      this._glyphCache[charcode] = glyph;
    }
    return glyph;
  }
  charsToGlyphs(chars) {