bug#56791: [PATCH] Add window arg to splitting commands, new commands to split root window

[Lars Ingebrigtsen <larsi@gnus.org>]

Hugo Heagren <hugo@heagren.com> writes:

> So, I have implemented:
> - a new optional argument on `split-window-right' and
>   `split-window-below' specifying /which/ window is to be split. This
>   defaults to the selected window. It also has no effect on the
>   interactive use of these functions, since the prefix argument is
>   still used for the SIZE arg.
> - new commands (implemented using this arg) which split the root window.
> - bound these commands to `C-x 7' and `C-x 9'. This seemed
>   appropriate, considering that these numbers were free, but the other
>   window-splitting commands are bound to numbers in that map.
> - (hopefully?) appropriate documentation changes
>
> Patches are attached. I don't know if Emacs has conventions for how
> large commits should be---mine are very atomic. Hope that works, but I
> could squash them down further and combine the messages if necessary.

Thanks; looks good to me.  I had some merging issues (since the affected
files have changed a bit since this patch series was proposed), so it
was easier for me to squash them before pushing to Emacs 29.