Bug 28316: (QA follow-up) Make clean_search_term public

Bug 28316: (QA follow-up) Make clean_search_term public

With all the work that's gone into improving the internal
_clean_search_term method I feel we should expose it publically as it's
going to be more widely helpful

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 641e8e4096b8d55afb534d593743154807f77221)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>