E.g:
```
ArrayHandle<Float64> doubleArray;
VariantArrayHandle varHandle{doubleArray};
ArrayHandleVirtual<Float32> = varHandle.AsVirtual<Float32>();
```
If there is a loss in range and/or precision, a warning is logged. If
the ValueTypes are Vecs with mismatched widths, an ErrorBadType is thrown.
Internally, an ArrayHandleCast is used between the VariantArrayHandle's
stored array and the ArrayHandleVirtual.
Query and report number of components at runtime so that it can work with
arrays of types with runtime varying number of components
Eg. ArrayHandleGroupVecVariable.
`vtkm::cont::testing` now initializes with logging enabled and support
for device being passed on the command line, `vtkm::testing` only
enables logging.
When you call VariantArrayHandle::CastAndCall, it now tries both basic
storage and virtual storage. You can modify the types of storages tried
by giving a type list of storage tags as the first argument.
ArrayHandleVirtual can automatically be constructed from any ArrayHandle.
In the cases where the input ArrayHandle doesn't derived from ArrayHandleVirtual,
it will automatically construct StorageAny to hold the array.
