R1:6d9776fa8963

Give EditEngine a Conduit-specific initialization pathway for objects

Summary:
Depends on D18845. See PHI243 for context and more details.

Briefly, some objects need a "type" transaction (or something similar) very early on, and we can't generate their fields until we know the object type. Drydock blueprints are an example: a blueprint's fields depend on the blueprint's type.

In web interfaces, the workflow just forces the user to select a type first. For Conduit workflows, I think the cleanest approach…