Add `Material Preview` option to `Material Output` Node

I have quite some materials that depend directly on object data (mostly in volumes), and then do not render intelligibly in the material previews, which makes them hard to sort/find.

Given that we already have a node Material Output , giving us the option to define different materials for different rendering outputs, I would love it if this had the option to make a separate material for Material Preview . I could then, for example, make a similar-colored surface shader in preview to keep track of my colored volume shaders that render badly in the preview.