Fields MVP

[Keavon]

Make the "Repeat" node call its predecessor (which provides the object to be repeated) once per repetition. In each repetition, it passes a different context (OwnedContextImpl), where the varargs has a different index: usize as position: DVec2 per instance. Then we use the (deduplication with stable node IDs? or caching?) if these are equivalent (because the index and position aren't accessed in the upstream nodes used as a lambda fields). TODO: More description.

[TrueDoctor]

You don't need to pass the index using varargs, we have an extra trait for index extraction