filenamesearch: use `ripgrep-all` if available
Original discussion: !336 (comment 1032743)
Use ripgrep-all
or ripgrep
as the default search backend for the filenamesearch KIO
slave, when searching file content and in local dirs. Only fallback to our own implementation
if they are not available.
The command line arguments are not hardcoded. Instead, filenamesearch
calls kio-filenamesearch-grep
that are installed in $BINDIR.
This allows users to easily customize the search backend by
having a script with the same name and higher precedence in $PATH.
(E.g. Change "rga -j2" to higher thread number for SSDs. Change whether
it respects ".gitignore" and ".ignore".)
Edited by Jin Liu