Previously, in order to copy an UnknownArrayHandle, you had to specify
some subset of types and then specially compile a copy for each potential
type. With the new ability to extract a component from an
UnknownArrayHandle, it is now feasible to precompile copying an
UnknownArrayHandle to another array. This greatly reduces the overhead of
using ArrayCopy to copy UnknownArrayHandles while simultaneously
increasing the likelihood that the copy will be successful.