It used to be the case where you needed to call `ResetTypes` on a
`VariantArrayHandle` before using `ArrayCopy` to limit the types it gets
compiled for. However, there is now a general form for
`UnknownArrayHandle`, so `ResetTypes` no longer does anything useful in
this case. Remove the use of that.

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.