Allow Cairo render to use Value Base as parameter on Circle Layer
Fix bug: Change interpolation doesn't work for exported parameters.
When casting a value node it is needed to check if the returned value node handle is valid because you can have a value node that is not the type you casted to. For example, a exported value node is first returned as layer parameter but from the dynamic parameters. See value_desc.cpp
Only show Interpolation contextual menu for layer parameters, layer parameter exported constant and exported value node constant.
Later when we teach the animated value nodes or other value nodes to change its interpolation, more conditions should be shown here.