Recursive broadcast

[ChrisRackauckas]

For unnecessarily odd containers in generic code, it would be useful to have a recursive version of broadcast that means "broadcast at the very bottom". That would make something like A ../ B work between two similar Vector{Vector{Matrix{Float64}}}s.

[tkelman]

duplicate of #20502

[ChrisRackauckas]

Almost. That wants to nest a known finitely many. I would like to have a "go to the bottom", where I may not know how many levels that is.