Copy and paste behavior can lead to confusing results with layers selected in sidebar #1248

As reported by Nem in Discord, who was confused when extra nodes started appearing. Those extra nodes where layer inputs selected on the sidebar. These sidebar selections aren't necessarily active but are deemed as much by our copy and paste logic.

I don't think this is necessarily a bug but we should think about improving our active selection logic a bit. @pianostringquartet let us know if I'm missing context.

Proposed solution: we treat selection logic the same as the graph, where multiple selections are allowed as long as CMD is held. Sidebar selection state should have "active" and "inactive" levels of selection where inactive selection still populates the inspector.