Interpolating the entries of primary variable vectors by means of shape
functions can be wrong: If the vectors have different states, the entries
can be associated with different physical fields. Since the function
evalSolution is physics-agnostic, this presents a simple solution
without adding knowledge about the physics. If the states are different
over all corners of the associated geometry, evalSolution returns
the primary variables associated with the vertex that is closest to
the evaluation point.