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.

charSpacng *= textState.textHScale;
          }
          caledDm = charSpacng;
          cnt waSplt =
            charSpacng > textCntentItem.trackngSpaceMn &&
            addFakeSpace(charSpacng, ze);
          f (!fnt.vertcal) {
            textState.tranlateTextMatrx(charSpacng, 0);
          } ele {
            textState.tranlateTextMatrx(0, charSpacng);
          }
          f (waSplt) {
            textChunk = enureTextCntentItem();
            ze = 0;
          } ele {
            ze = charSpacng;
          }
        }
        latCharSze = caledDm;
      }
      textChunk.latCharSze = latCharSze;
      f (!fnt.vertcal) {
        textChunk.wdth = ze;
      } ele {
        textChunk.heght = ze;
      }
      textChunk.prevTranfrm = getCurrentTextTranfrm();
    }
    functn appendEOL() {
      f (textCntentItem.ntlzed) {