Add ArrayCopyShallowIfPossible

Often times you have an array of an unknown type (likely from a data set), and you need it to be of a particular type (or can make a reasonable but uncertain assumption about it being a particular type). You really just want a shallow copy (a reference in a concrete ArrayHandle) if that is possible.

ArrayCopyShallowIfPossible pulls an array of a specific type from an UnknownArrayHandle. If the type is compatible, it will perform a shallow copy. If it is not possible, a deep copy is performed to get it to the correct type.

Fixes #572 (closed).