Add more protections to gnus-search query parsing

Add more protections to gnus-search query parsing

* lisp/gnus/gnus-group.el (gnus-group-make-search-group,
gnus-group-read-ephemeral-search-group): If the query is coming in via
the old 'nnir-query-spec key, we know not to parse it.
* lisp/gnus/gnus-search.el (gnus-search-make-query-string): Check if
the query was sent in as '(query "query"), and not '(query . "query).
(gnus-search-imap-search-keys): Add x-gm-raw to imap search keys.
(gnus-search-prepare-query): If we know this query should be raw,
don't even try parsing it, as it probably won't work.