Fix handling of cell fields in Tube filter

The Tube filter wraps a tube of polygons around poly line cells. During this process it had a strange (and wrong) handling of cell data. It assumed that each line had an independent field entry for each segment of each line. It thus had lots of extra code to find the length and offsets of the segment data in the cell data.

This is simply not how cell fields work in VTK-m. In VTK-m, each cell has exactly one entry in the cell field array. Even if a polyline has 100 segments, it only gets one cell field value. This behavior is consistent with how VTK treats cell field arrays.

The behavior the Tube filter was trying to implement was closer to an "edge" field. However, edge fields are currently not supported in VTK-m. The proper implementation would be to add edge fields to VTK-m. (This would also get around some problems with the implementation that was removed here when mixing polylines with other cell types and degenerate lines.)