ENH: Update selected Filters/Sources to support DesiredOutputPrecision

This updates selected sources to support a choice of desired precision
(single or double) for output points. It uses the analogous code in
vtkThreshold as a model.

Change-Id: If616db48b3d979b7ac01d3b5200fff523b06a26b
Merge topic 'filters-sources-desired-output-precision' into master

28976fd3 ENH: Update selected Filters/Sources to support DesiredOutputPrecision