Previously, all of the `ArrayGetValues` implementations were templated
functions that had to be built. That meant that any code using them had
to be compiled with a device compiler and create special code for it.
This change uses an `UnknownArrayHandle` to encapsulate the
`ArrayHandle` and call a per-compiled library function. This means that
the code only has to be compiled once.
This method is a remenant of when `ArrayHandle` could only store data on
one device at a time. It is now capable of storing data on any number of
devices (as well as the host), so asking for "the" device no longer
makes sense. Thus, this method is deprecated in favor of
`ArrayHandle::IsOnDevice`.
This deprecation leads to fixing some older functionality that still
assumed data could only be on one device at a time.
Fixes#592.
