Preserve dimensions in `stack`, `vcat`

I want to preserve dimensions.

julia> let
           ka = KeyedArray(
               rand(4,3);
               a=[1,2,1,2],
               b=1:3,
           )
           stack([ka, ka])
       end
4×3×2 Array{Float64, 3}:
[:, :, 1] =
 0.157501  0.15453   0.236119
 0.62595   0.142494  0.503847
 0.646891  0.829133  0.323376
 0.487593  0.930134  0.338322

[:, :, 2] =
 0.157501  0.15453   0.236119
 0.62595   0.142494  0.503847
 0.646891  0.829133  0.323376
 0.487593  0.930134  0.338322

Reproduce the Julia example with KeyedArray and compare the current results of stack and vcat. Inspect the implementations or entry points for those operations and any nearby tests; done means the resulting arrays retain the relevant keyed dimensions rather than returning only plain dimensions.