Have a way to query a particular entity type only in hierarchy

[smitpatel]

Currently when user query for some entity type in database, we always get results for that entity type and all derived types. Using OfType and is operator filter out the type but unless the resulting type is leaf type, it will still fetch derived type. Only way to filter out to get particular type is use discriminator property (or GetType, see #13424) but it requires processing to remove additional tables for TPC/TPT. We can expose that processing via some first-class operator to users.