Sometimes it's useful to pass around a set of values with a generic
type. The virtual array data structures allow this, but they don't
have logical ownership. My initial use case for this is as a return
type for the functions that interpolate curve attributes to evaluated
points, but a need for this data structure has come up in a few other
places as well. It also reduced the need for templates.
Differential Revision: https://developer.blender.org/D11103
