Enqueue DVU when modifying or creating attribute func bindings for variants with existing components

[britmyerss]

One other change here to discuss Monday:

• When resetting an attribute prototype, if the prototype is for a Prop, default to the unset intrinisic func
• If it's for an output socket, reset to the identity func, so that regenerate can re-set the prototype to a value from if it's defined in the asset definition func

Update: discussed and we are not going to do this as it prevents that prop from ever having a default value again (under current constraints)