Resolve "Disable lighting in Slice representation"
Lighting on the Slice representation has the undesirable effect of darkening the Slice with the default light, which is off center with respect to the view and focal points. We assume the common use case for this representation is to view the data as directly as possible to match colors on the slice with colors in the color legend. To better support this use case, lighting is disabled for this representation.
Closes #17236 (closed)