sql: test purge of search tokens (#86527)

introduce a new mechanism to implement FTS with fuzzy-match.
This is made possible by adding and maintaining a table of the
FTS tokens, wcs_search_tokens, fed with searchable_formdefs
and wcs_all_forms.
When a query is issued, its tokens are matched against the
tokens with a fuzzy match when no direct match is found, and
the query is then rebuilt.

wcs/sql.py

@@ -1762,7 +1762,7 @@ WITH
                          tsquery_agg_or(plainto_tsquery(partial.token)),
                          plainto_tsquery(word)) AS tokens
             FROM tokenized
-            LEFT JOIN wcs_search_tokens AS partial ON partial.token % plainto_tsquery(word) AND word not similar to '%[0-9]{2,}%'
+            LEFT JOIN wcs_search_tokens AS partial ON partial.token % plainto_tsquery(word)::text AND word not similar to '%[0-9]{2,}%'
             GROUP BY word)
 SELECT tsquery_agg_and(tokens) FROM super_tokenized;
 $function$;"""