Add min/max and 0 as param possibilities for reflect transform

[nicolemarsaglia]

This is two issues in one:

1. If a user wants to reflect over y=0, where x and z are also zero, you get a nan when we normalize resulting in a blank image: https://github.com/Alpine-DAV/ascent/blob/develop/src/libs/vtkh/filters/PointTransform.cpp#L113

potential fixes: force return of (0,0,0), or 2D case set a 1 for the unused axis, (0,0,1), but that feels like bad math.

2. Add capability for user to reflect over y=max, y=min, x=max, etc. , rather than having to know the exact dims. Runs into the same issues as above if min or max is 0. Do we need to add/subtract epsilon under the covers to avoid overlap?