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.