Query: report the elementId Convert writes, so results join a converted graph

[someshSandbox]

A Query result can't be matched to the element Convert writes for it. Each reports a different identity, and the id Convert writes is not a queryable property.

// lib.sysml
package Lib { part def Engine { attribute mass : ScalarValues::Real; } }
// app.sysml
package App { private import Lib::*; part e : Engine; }

After ParseSources of both documents (develop 62f2442c3):

element	Query (select: ["@id", "qualifiedName"])	Convert to api-json, @id
Lib	Lib	Lib
Lib::Engine	Lib::Engine	Lib__Engine
Lib::Engine::mass	Lib::Engine::mass	Lib__Engine__mass
App::e	App::e	App__e
ScalarValues::Real (scope: ["ScalarValues::Real"])	ScalarValues::Real	14c0aa22-5489-59b5-b438-ded26e83ba31 (normative id)

QueryResultElement.id is documented as the qualified name, "the identity this service reports", so this is by design. But select: ["elementId"] is refused (unknown query property "elementId"), and the qualified name maps to the written @id only through the writer's escaping. For a library element it doesn't map at all, since that id is a hash. A declared ElementId or -id uuid also changes the written id.

Request. Make elementId a queryable (selectable) property. It would report the id Convert writes for the element under the same id form: the declared id, the derived qualified-form id, or a library element's normative id. The two answers can then be joined without re-deriving ids on the client.