Declaration names sounds like a name of declaration -- something you
can use for analysis. It empathically isn't, and is just a label
displayed in various UI. It's important not to confuse the two, least
we accidentally mix semantics with UI (I believe, there's already a
case of this in the FamousDefs at least).
Currently a method only has defaultness if it is a provided trait
method, but this will change when specialisation is available and may
need to become a concept known to hir.
I opted to go for a 'fewest changes' approach given specialisation is
still under development.