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.

originalCharCode,
    fontChar,
    unicode,
    accent,
    width,
    vmetric,
    operatorListId,
    isSpace,
    isInFont
  ) {
    return (
      this.originalCharCode === originalCharCode &&
      this.fontChar === fontChar &&
      this.unicode === unicode &&
      this.accent === accent &&
      this.width === width &&
      this.vmetric === vmetric &&
      this.operatorListId === operatorListId &&
      this.isSpace === isSpace &&
      this.isInFont === isInFont
    );
  }
}
function int16(b0, b1) {