Rather than force all dispatchers to be templated on a device adapter,
instead use a TryExecute internally within the invoke to select a device
adapter.
Because this removes the need to declare a device when invoking a
worklet, this commit also removes the need to declare a device in
several other areas of the code.
The ScalarsToColors is the first step in reproducing the color
capability that exists in VTK. The next step after this is to
provide a comparable lookup table.