Enable registering notifiers for newly created objects

[sync-by-unito]

Currently objects can't be observed in the same write transaction as they were created in, which is sometimes inconvenient. This is due to that ObjKey is not actually a stable identifier until a write transaction is committed. If an object is created then the write is rolled back, the ObjKey will be reused by the next object created in the next write transaction.

Supporting this probably requires some sort of deferred notifier registration for notifiers created inside a write transaction. If the write is rolled back, notifiers which depend on objects that no longer exist would either be not registered or somehow act as if the object was deleted. This is mostly complicated for Results notifiers, which may need to rewrite the associated Query?