Refactor FileSearchQuery and create base class SearchQuery
Summary: As discussed in T10521, it is useful to refactor out the generic query building logic in FileSearchQuery and create the base class SearchQuery. This would allow us to create other domain specific queries without having to reimplement all the building logic, as will be the case with TeamdriveSearchQuery.
Test Plan: All tests defined in FileSearchQueryTest should remain valid and, as of this patch, passing.
Reviewed By: dvratil
Subscribers: kde-pim, LibKGAPI
Maniphest Tasks: T10521
Differential Revision: https://phabricator.kde.org/D19490