Remove use of utf8::iterator in regex execution
Remove use of utf8::iterator in regex execution

This avoids having two copies of the subject string bounds, one
in the ExecConfig and one in the utf8 iterator.

lenormf/kakoune,Somasis/kakoune,danr/kakoune,alexherbo2/kakoune,occivink/kakoune,occivink/kakoune,casimir/kakoune,casimir/kakoune,jkonecny12/kakoune,lenormf/kakoune,casimir/kakoune,danr/kakoune,jkonecny12/kakoune,occivink/kakoune,Somasis/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,jjthrash/kakoune,jkonecny12/kakoune,occivink/kakoune,Somasis/kakoune,danr/kakoune,mawww/kakoune,jjthrash/kakoune,alexherbo2/kakoune,mawww/kakoune,danr/kakoune,casimir/kakoune,lenormf/kakoune,jjthrash/kakoune,Somasis/kakoune,alexherbo2/kakoune,jjthrash/kakoune,mawww/kakoune,mawww/kakoune,lenormf/kakoune