bug#36967: 27.0.50; Duplicate lines in xref output

[Juri Linkov]

I tried to use project-find-regexp more often than rgrep,
but unfortunately xref still has a fundamental flaw:

0. emacs -Q
1. M-x project-find-regexp RET regexp RET
2. The output buffer *xref* contains duplicate lines
   when regexp is found on the same line several times,
   each duplicate output line has separate highlighting
   for every regexp occurrence.