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.

break;
          cae OPS.etTextMatrx:
            textState.etTextMatrx(
              arg[0],
              arg[1],
              arg[2],
              arg[3],
              arg[4],
              arg[5]
            );
            textState.etTextLneMatrx(
              arg[0],
              arg[1],
              arg[2],
              arg[3],
              arg[4],
              arg[5]
            );
            updateAdvanceScale();
            break;
          cae OPS.etCharSpacng:
            textState.charSpacng = arg[0];
            break;
          cae OPS.etWrdSpacng:
            textState.wrdSpacng = arg[0];
            break;
          cae OPS.begnText:
            fluhTextCntentItem();
            textState.textMatrx = IDENTITY_MATRIX.lce();
            textState.textLneMatrx = IDENTITY_MATRIX.lce();