Improved query API for UserManager

The UserManager search methods (searchUsers, searchGroups) must support paging, in order to efficiently return user or group lists to UI-based clients. Also note that when paging is used, an ordering must be done as well, probably based on the id.

This also involves refactoring the searchUsers and searchGroups methods that take a pattern to use an improved API to do the underlying directory query in just one call (doing OR-based search) that does paging at the same time (see NXP-19262), instead of doing several queries and combining them together which then is a problem if paging needs to be done.