Initially, the probe filter would simply not set a value if a sample was
outside the input `DataSet`. This is not great as the memory could be
left uninitalized and lead to unpredictable results. The testing
compared these invalid results to 0, which seemed to work but is
probably unstable.
This was partially fixed by a previous change that consolidated to
mapping of cell data with a general routine that permuted data. However,
the fix did not extend to point data in the input, and it was not
possible to specify a particular invalid value.
This change specifically updates the probe filter so that invalid values
are set to a user-specified value.
Now that the dispatcher does its own TryExecute, filters do not need to
do that. This change requires all worklets called by filters to be able
to execute without knowing the device a priori.
This commit removes `vtkm::filter::Result`. All methods that used
`vtkm::filter::Result` simply change to use `vtkm::cont::Dataset` instead.
The utility API on `Result` that was used to add fields to the resulting
dataset is now available via `vtkm::filter::internal::CreateResult`.
