* Introduce a generalized feature toggle system that uses user
preferences or localStorage for anons (right now the latter is out
of scope but will be explored in a follow up)
* Feature flagged to VisualEnhancementNext for now, given the dependency
on icon size
Bug: T319449
Change-Id: I7343a3f38b720411d5ef5f3414f25f475b0bb84a
