Fix inference for column broadcasting

[charleskawczynski]

It turns out that what was missing here is that column on broadcasted objects passes nothing to the axes. So, even though we call instantiate on the broadcasted objects in the Fields broadcasting:

@inline function Base.copyto!(
    dest::Field,
    bc::Base.Broadcast.Broadcasted{<:AbstractFieldStyle},
)
    copyto!(field_values(dest), Base.Broadcast.instantiate(todata(bc)))
    return dest
end

We later call column inside the datalayouts loop:

function Base.copyto!(
    dest::VIJFH{S, Nv, Nij, Nh},
    bc::BroadcastedUnionVIJFH{S, Nv, Nij, Nh},
    ::ToCPU,
) where {S, Nv, Nij, Nh}
    # copy contiguous columns
    @inbounds for h in 1:Nh, j in 1:Nij, i in 1:Nij
        col_dest = column(dest, i, j, h)
        col_bc = column(bc, i, j, h)
        copyto!(col_dest, col_bc)
    end
    return dest
end

Which then drops the axes and passes in nothing. This results in looking up the axes inside getindex rather than column.

I'm kind of surprised that this wasn't a more wide spread issue. Also, it oddly didn't seem to have a performance benefit, but at least it fixes inference and conceptually makes more sense this way.

Closes #1981.