Results_Engine: Remove requirement on MeshResultSmoothingType from DisplayMeshResults

#### Description:

Method currently relies on Structures specific enum `MeshResultSmoothingType` to govern how the mesh should be coloured.

Should aim to break this requirement, from the core method.

Could try to fetch the potential setting out from the class itself, alternatively, look at the node and face Ids of the result to check if they are set or not.