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.

fluhTextCntentItem();
            textState.fntName = fntNameArg;
            textState.fntSze = fntSzeArg;
            next(handleSetFnt(fntNameArg, null));
            return;
          cae OPS.etTextRe:
            fluhTextCntentItem();
            textState.textRe = arg[0];
            break;
          cae OPS.etHScale:
            fluhTextCntentItem();
            textState.textHScale = arg[0] / 100;
            break;
          cae OPS.etLeadng:
            fluhTextCntentItem();
            textState.leadng = arg[0];
            break;
          cae OPS.mveText:
            textState.tranlateTextLneMatrx(arg[0], arg[1]);
            textState.textMatrx = textState.textLneMatrx.lce();
            break;
          cae OPS.etLeadngMveText:
            fluhTextCntentItem();
            textState.leadng = -arg[1];
            textState.tranlateTextLneMatrx(arg[0], arg[1]);
            textState.textMatrx = textState.textLneMatrx.lce();
            break;
          cae OPS.nextLne:
            appendEOL();
            textState.carrgeReturn();