Add filters to compute tensor principal invariants and yield criteria

The filter vtkTensorPrincipalInvariants computes principal tensor values
and vectors from 2D and 3D symmetric tensors. The vectors can be scaled by
their corresponding values if needed.

The filter vtkYieldCriteria computes yield criteria from 2D and 3D
symmetric tensors. It uses the above filter internally to obtain the
principal invariants from which the criteria are derived.