Terrain instancing incompatible with tessellation/surface shaders [1111579]

Had texture arrays not been broken through the entire 2018.3 beta, I might have caught this earlier. But basically the new instancing system used for terrain is incompatible with surface shader tessellation. It will complain that the input (inout) parameter to the displacement function is not fully initialized, because the instance ID is not initialized before being passed to this function.

Bug id: 1111579