Add VTK_COLOR_MODE_DIRECT_SCALARS. See vtkScalarsToColors::MapScalars.

Change-Id: I0fa7d8dde623b19204397d259e0c63f7d5bc4b66
Add a test for VTK_COLOR_MODE_DIRECT_SCALARS

Change-Id: I9ddbc050bd4cdb0c9dafaed55dd427b84f8a551c
Merge topic 'map-scalars-14943' into master

2d61deaa Add a test for VTK_COLOR_MODE_DIRECT_SCALARS
00de9a94 Add VTK_COLOR_MODE_DIRECT_SCALARS. See vtkScalarsToColors::MapScalars.