Docsystem doesn't work with nospecialize

[timholy]

The docsystem thinks these two methods are the same despite Julia itself knowing better:

julia> module DS

       """
       `f` for Numbers
       """
       f(@nospecialize(x::Number)) = 1

       """
       `f` for arrays
       """
       f(@nospecialize(x::AbstractArray)) = 2

       end
┌ Warning: Replacing docs for `Main.DS.f :: Tuple{Any}` in module `Main.DS`
└ @ Base.Docs docs/Docs.jl:223
Main.DS

help?> DS.f
  f for arrays

julia> DS.f(1)
1

julia> DS.f([1])
2