rewrite_generic doesn't support splatting

[odow]

julia> using MutableArithmetics; const MA = MutableArithmetics
MutableArithmetics

julia> x = [1, 2, 3]
3-element Vector{Int64}:
 1
 2
 3

julia> @macroexpand MA.@rewrite(+(x...))
quote
    #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:321 =#
    let
        #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:322 =#
        begin
            begin
                var"#5###278" = (MutableArithmetics.MutableArithmetics).Zero()
                var"#6###277" = (MutableArithmetics.MutableArithmetics).operate!!((MutableArithmetics.MutableArithmetics).add_mul, var"#5###278", x...)
            end
        end
        #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:323 =#
        var"#6###277"
    end
end

julia> @macroexpand MA.@rewrite(+(x...), move_factors_into_sums = false)
quote
    #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:321 =#
    let
        #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:322 =#
        begin
            #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:317 =#
        end
        #= /Users/oscar/.julia/dev/MutableArithmetics/src/rewrite.jl:323 =#
        x...
    end
end