Items under Components are rendered in state preview

Instances under a Component instance, either explicit or implicit (e.g. an implicit delegate item given as a child of a Repeater), are rendered in state preview. They are also rendered in form editor if unified rendering path is enabled.

The problem is that even though the component is correctly handled as a component, its descendants still get regular items created for them.

This is difficult to fix properly, as we don't know the eventual parent at creation time. We could maybe permanently hide the unnecessary instances, though.