Followup to
COR-770: Functionality is there, but there's still some loose ends:
- code duplication among #defrag*() methods in *Handler0
- ArrayHandler hierarchy looks inappropriate now
- writing to readOnly database on #storedClasses() call has naively been disabled with config check
- duplication of primitive array fields on .NET < 6.3 in format migration test cases is simply ignored (by using the field count from slot)
COR-1083is about wrapping upCOR-770implementation code