[MLDataDevices] devices don't preserve identity

[CarloLucibello]

I was under the impression that these used to return true

julia> cdev = cpu_device()
(::CPUDevice) (generic function with 2 methods)

julia> cdev(x) === x
false

julia> gdev = gpu_device()
(::CUDADevice{Nothing}) (generic function with 2 methods)

julia> a = gdev(x)
2-element CuArray{Float32, 1, CUDA.DeviceMemory}:
 0.048840165
 0.6700894

julia> a === gdev(a)
false

[avik-pal]

This is coming from:

julia> x = rand(3, 3)
3×3 Matrix{Float64}:
 0.0299446  0.637261   0.0907949
 0.877796   0.0118281  0.0779904
 0.708503   0.445012   0.690353

julia> Array(x) === x
false

[avik-pal]

We need to add dispatches to avoid this for all the devices (except reactant where ConcreteRArray already implements this)