Fix broadcast assignment for VectorOfArray with StructArrays

[jlchan]

Attempt 2 to address SciML/OrdinaryDiffEq.jl#2625 (comment). I just applied the same approach taken in #425 for setindex! to broadcasted Base.copyto!.

I've verified that this also fixes the discrepancy in number of time-steps taken by an adaptive solver. The following MWE now results in the same number of accepted time-steps under this PR.

using OrdinaryDiffEqSSPRK, RecursiveArrayTools
using StaticArrays, StructArrays

function rhs!(du_voa, u_voa, params, t)
    du = parent(du_voa)
    u = parent(u_voa)
    du .= u
end

# StructArray storage
u = StructArray{SVector{1, Float64}}(ntuple(_ -> [1.0, 2.0], 1))
ode = ODEProblem(rhs!, VectorOfArray(u), (0, 0.7))
sol_SA = solve(ode, SSPRK43())
@show sol_SA.stats.naccept

# Vector{<:SVector} storage
u = SVector{1, Float64}.([1.0, 2.0])
ode = ODEProblem(rhs!, VectorOfArray(u), (0, 0.7))
sol_SV = solve(ode, SSPRK43())
@show sol_SV.stats.naccept

[jlchan]

@ChrisRackauckas do you know if the integration CI failures are spurious? The error messages don't appear to involve StructArrays, but I'm not sure if inference failures like IntegrationTest / DiffEqBase.jl/Downstream/1 (pull_request) are related.

[ChrisRackauckas]

Spurious, I need to work through those.