A ValueNode that will update its value from its "initial" input to its "end" input
according to the given input within expected range [0, 1]. For example MappingNode could
accept values emmited by InterpolatorNode. The node can also extrapolate beyond the
output range if input goes beyond the expected input range.
This node should calculate and set a new value based on frame time and its parents (the nodes
it depends on). When this is called, it's guaranteed that the parent nodes have already been
updated for this frame.