The dist2 values used by the pred/lift attribute coding schemes is
dependent upon the distances between points in the point cloud.  Using
the --positionQuantizationScale option to scale the input point cloud
therefore affects the required dist2 values.

This commit adds the --positionQuantizationScaleAdjustsDist2=1|0 option
to simplify the configuration of dist2.  When enabled, the encoder will
automatically scale any dist2 values by the squared position scale
factor.