Unexpected behavior of deepcopy of an OffsetArray{<:Any, <:Any, <:MtlArray}

[simone-silvestri]

Playing around with Metal I can across some unexpected behavior with OffsetArrays of MtlArrays concerning deepcopy:

julia> a = MtlArray(zeros(Float32, 2));

julia> a = OffsetArray(a, -1);

julia> b = deepcopy(a);

julia> fill!(b, 1);

julia> a
2-element OffsetArray(::MtlVector{Float32, Metal.PrivateStorage}, 0:1) with eltype Float32 with indices 0:1:
 1.0
 1.0

Note that this does not happen on pure MtlArrays

julia> a = MtlArray(zeros(Float32, 2));

julia> b = deepcopy(a);

julia> fill!(b, 1);

julia> a
4-element OffsetArray(::MtlVector{Float32, Metal.PrivateStorage}, 0:3) with eltype Float32 with indices 0:3:
 0.0
 0.0

Nor with OffsetArrays of other types:

julia> a = OffsetArray(zeros(2), -1);

julia> b = deepcopy(a);

julia> fill!(b, 1);

julia> a
2-element OffsetArray(::Vector{Float64}, 0:1) with eltype Float64 with indices 0:1:
 0.0
 0.0

[maleadt]

Seems to work with this definition: https://github.com/JuliaGPU/CUDA.jl/blob/2bf90de1dce7fd58d6ad6cf6b8ff4525e0ad6961/src/array.jl#L180-L183

I wonder if we could move this to GPUArrays? Mind taking a stab at this?