custom search pages don't act like /@@search due to munge_search_term

[djay]

Now that volto allows creating custom search forms it doesn't make sense that we should be using .contains for this as it does things like add a wildcard to the end of the char and prevent

• see https://github.com/plone/plone.app.querystring/blob/f8bfbfa814d63fda9bef94d79dc88f55235eaf58/plone/app/querystring/querybuilder.py#L204
• and https://github.com/plone/plone.app.search/blob/master/plone/app/search/browser.py#L22

I think there should be a new .string.search operator which does the same kind of processing as @@search does. e.g. not add a wildcard to the end and not put AND operator in