OrderedDict should rehash on deepcopy (like Dict does)

[Keno]

Compare:

julia> mutable struct ConstIdentity
       end

julia> dict = OrderedDict{ConstIdentity, Int64}()
Dict{ConstIdentity, Int64}()

julia> dict[ConstIdentity()] = 1
1

julia> dict[ConstIdentity()] = 2
2

julia> all(haskey.((dict,), keys(dict)))
true

julia> dict2 = deepcopy(dict)
OrderedDict{ConstIdentity, Int64} with 2 entries:
  ConstIdentity() => 1
  ConstIdentity() => 2

julia> all(haskey.((dict2,), keys(dict2)))
false

vs Dict:

julia> mutable struct ConstIdentity
       end

julia> dict = Dict{ConstIdentity, Int64}()
Dict{ConstIdentity, Int64}()

julia> dict[ConstIdentity()] = 1
1

julia> dict[ConstIdentity()] = 2
2

julia> all(haskey.((dict,), keys(dict)))
true

julia> dict2 = deepcopy(dict)
Dict{ConstIdentity, Int64} with 2 entries:
  ConstIdentity() => 1
  ConstIdentity() => 2

julia> all(haskey.((dict2,), keys(dict2)))
true

We need to override deepcopy_internal to rehash like base does:
https://github.com/JuliaLang/julia/blob/13155226e11fa025be5d4d3033d25c1091b35887/base/deepcopy.jl#L141-L156