Support testing chunked forward mode

Consider this (From #36)

simo(x) = (x, 2x)
function ChainRulesCore.frule((_, ẋ), simo, x)
    y = simo(x)
    return y, Composite{typeof(y)}(ẋ, 2ẋ)
end

I believe that that the following should work:

frule_test(simo, (randn(), randn(4)))  # chunked mode, scalar/vector
frule_test(simo, (randn(3), randn(2, 3)))  # chunked mode, vector/matrix

as I believe the following is the correct chunked mode behavour.
@YingboMa am i right?

at least for the scalar primal and vector differential

julia> frule((Zero(), [1, 2, 3]), simo, π)
((π, 6.283185307179586), ([1, 2, 3], [2, 4, 6]))

julia> frule((Zero(), [1 1; 0 1; 1 0]), simo, [1, 1, 1])
(([1, 1, 1], [2, 2, 2]), Composite{Tuple{Array{Int64,1},Array{Int64,1}}}([1 1; 0 1; 1 0], [2 2; 0 2; 2 0]))

Start with the existing frule_test calls and the frule examples shown in this issue, then review the discussion in #36. Determine the expected chunked forward-mode behavior for scalar/vector and vector/matrix inputs, and confirm that frule_test accepts both cases with the demonstrated outputs.