interpolation: Optimise by using particle local coordinates

This change changes the point-tetIndices-face interpolation function
method to take barycentric-tetIndices-face arguments instead. This
function is, at present, only used for interpolating Eulerian data to
Lagrangian particles.

This change prevents an inefficiency in cellPointInterpolation whereby
the position of the particle is calculated from it's barycentric
coordinates, before immediately being converted back to barycentric
coordinates to perform the interpolation.