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 (!properties.fontMatrix) {
    return;
  }
  if (properties.fontMatrix[0] === FONT_IDENTITY_MATRIX[0]) {
    return;
  }
  
  const scale = 0.001 / properties.fontMatrix[0];
  const glyphsWidths = properties.widths;
  for (const glyph in glyphsWidths) {
    glyphsWidths[glyph] *= scale;
  }
  properties.defaultWidth *= scale;
}
function adjustToUnicode(properties, builtInEncoding) {