Search: match all results against DB first to exclude invalid results

In some cases the search backend can return results that actually
no longer exist in Akonadi DB (for example because the indexer is
busy indexing something else while an Item was removed, which triggered
search update), or because it went out-of-sync with the DB due to
a bug or manual cleanup. This lead to a lots of (albeit harmless)
foreign key constraint errors as we tried to insert items into
CollectionPimItemRelation table which did not exist in PimItemTable.
To prevent this we first match the results against PimItemTable to
get only the existing Items (we need them anyway for change ntf)
and then insert only those into the CollectionPimItemRelation table.

This does not fix problems with search updates unfortunately.

CCBUG: 353675