BUG: Fix interpolated point in cloth grab

This moves a few things around but fixes: 1.) The interpolated point was using 0 in all index. https://gitlab.kitware.com/andrew.wilson/iMSTK/-/blob/master/Examples/PBD/PBDClothGrab/pbdClothGrabExample.cpp#L346

2.) The barycentric coordinates stored in triangleSelectionPtUvw was being overrwitten on later iterations of ray-triangle intersection checks. https://gitlab.kitware.com/andrew.wilson/iMSTK/-/blob/master/Examples/PBD/PBDClothGrab/pbdClothGrabExample.cpp#L289

Also drops the resolution down to 4x4 so its more noticable that it can grab points intermediately in triangles.