The testing files (even the headers) are not available if
`VTKm_ENABLE_TESTING` is off.
Mostly, the testing was used to generate example data sets. Instead,
change the examples to load data files.
There was an error that caused deprecation warnings in VTK-m to be
suppressed, which meant that many uses of deprecated features went
unnoticed. This fixes those deprecation warnings.
The majority of the warnings were caused by the use of the deprecated
`Cast`, `CopyTo`, and `ResetTypes` methods of `UnknownArrayHandle` (or
`VariantArrayHandle`). Both `Cast` and `CopyTo` have been subsumed by
`AsArrayHandle` (to make the functionality more clear). `ResetTypes` now
requires a second template argument to define the storage types to try.
Also fixed some issues with `SerializableField` being deprecated.
This class is no longer necessary because `Field` can now be directly
serialized.
By removing the ability to have multiple CellSets in a DataSet
we can simplify the following things:
- Cell Fields now don't require a CellSet name when being constructed
- Filters don't need to manage what the active cellset is