Fix VisualActor tech changes for mirages
Correctly recompute the actor when something changes that could modify it (ownership change, ...).
Make sure mirages are updated when they reappear after being hidden.
Make sure foundations have proper identity classes.
Make sure mirages don't respond to value modifications in the visual component.
Clarify a few comments.
Earlier work by: Sandarac
Differential Revision: https://code.wildfiregames.com/D576