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

  plone.app.querystring/plone/app/querystring/querybuilder.py

  Line 204 in f8bfbfa

  r = quote_chars(r) + '*'

• 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