Do not require `VecTraits` for `UnknownArrayHandle` components

Whan an UnknownArrayHandler is constructed from an ArrayHandle, it uses the VecTraits of the component type to construct its internal functions. This meant that you could not put an ArrayHandle with a component type that did not have VecTraits into an UnknownArrayHandle.

UnknownArrayHandle now no longer needs the components of its arrays to have VecTraits. If the component type of the array does not have VecTraits, it treats the components as if they are a scalar type.