The primary (likely only) use of PointTransform is to perform affine
transform on the position of the mesh. However, PointTransform did not
actually move the mesh. Rather, it just created a new field with the
transformed points.
Now, the output has its coordinate system replaced with the transformed
one generated (in addition to be added as a field). This can be turned
off (but defaults to on).
Also changed the constructor to turn on UseCoordinateSystemAsField so
that by default the filter operates on the existing coordinate system
and replaces it with the new coordinate system.
Also removed the template parameter on the filter. That added an
unnecessary complication to using it.
