We are moving to deprecate `ArrayHandleVirtual`, so we are removing the
feature where `VariantArrayHandle::CastAndCall` automatically casts to
an `ArrayHandleVirtual` if possible.

The big reason to make this change now (as opposed to later when
`ArrayHandleVirtual` is deprecated) is to improve compile times.
This prevents us from having to compile an extra code path using
`ArrayHandleVirtual`.