Add gather(d::DArray{T,N,Array{T,N}}) where {T, N}

I am wondering why it is not possible to gather a DArray{T,N,Array{T,N}}?

I wrote this method to the gather function, it works for my purpose. Maybe it is possible to add it? (or maybe I did a mistake and it should be changed somehow?)
```
function gather(d::DArray{T,N,Array{T,N}}) where {T, N}
a=Array{T}(undef, size(d))
indices = collect.(d.indices)
@sync for (i,p) in enumerate(procs(d))
@async a[indices[i]...] = remotecall_fetch(localpart, p, d)
end
a
end
```

Start by locating the existing gather function and the DArray definition in DistributedArrays.jl, then compare current gather methods with the proposed DArray{T,N,Array{T,N}} signature. Verify the behavior with a distributed array whose local parts use Array storage; done means gather returns the expected Array with all distributed indices populated.

Written by the indexing model from the issue text.