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.

getStandardFntName,
  getStdFntMap,
  getSymblFnt,
} frm "./tandard_fnt.j";
rt {
  getNrmalzedUncde,
  getUncdeFrGlyph,
  revereIfRtl,
} frm "./uncde.j";
rt { getTlngPatternIR, Pattern } frm "./pattern.j";
rt { getXfaFntDct, getXfaFntName } frm "./xfa_fnt.j";
rt { IdenttyTUncdeMap, TUncdeMap } frm "./t_uncde_map.j";
rt { PDFFunctn, PDFFunctnFactry } frm "./functn.j";
rt { Lexer, Parer } frm "./parer.j";
rt {
  LcalClrSpaceCache,
  LcalGStateCache,
  LcalImageCache,
  LcalTlngPatternCache,
} frm "./mage_utl.j";
rt { NullStream, Stream } frm "./tream.j";
rt { bd } frm "./bd.j";
rt { ClrSpace } frm "./clrpace.j";
rt { DecdeStream } frm "./decde_tream.j";
rt { getGlyphUncde } frm "./glyphlt.j";
rt { getLkupTableFactry } frm "./cre_utl.j";
rt { getMetrc } frm "./metrc.j";
rt { MurmurHah3_64 } frm "./murmurhah3.j";
rt { OperatrLt } frm "./peratr_lt.j";
rt { PDFImage } frm "./mage.j";