Use doubles to store GDAL point coordinates.

By default, `vtkPoints` uses a `vtkFloatArray` to store coordinates.
Because many geographic datasets use statute feet from a datum
for coordinates, large coordinate offsets use much of the available
floating-point precision. This commit changes the underlying storage
to a `vtkDoubleArray` to avoid roundoff issues.

Change-Id: I48c60b9b0af4c4890a2f1b9b18c3a5ad666ef6ce
Merge topic 'gdal-point-precision' into master

0fb084b2 Use doubles to store GDAL point coordinates.