`focus output <direction>` (and `focus <direction>` across outputs) considers only one axis

## I'm submitting a…

[ ] Bug

[x] Feature Request

[ ] Documentation Request

[ ] Other (Please describe in detail)

## Current Behavior
Consider the following XRandR layout:


When focus is on output 1, `focus output right` moves focus to 2.

This seems to be because i3 [considers only one axis](https://github.com/i3/i3/discussions/5516#discussioncomment-6017571) when choosing the best output to focus.

## Desired Behavior
I think moving the focus to 3 would be less surprising.

## Impact

[ ] This feature requires new configuration and/or commands

## Environment

Output of `i3 --moreversion 2>&-`:

Binary i3 version:  4.20.1-78-ga661d82c © 2009 Michael Stapelberg and contributors

Running i3 version: 4.20.1-78-ga661d82c (pid 2570446)

Loaded i3 config:

  /home/vladimir/.i3/config (main) (last modified: 2023-05-27T09:33:08 UTC, 0 seconds ago)


The i3 binary you just called: /usr/bin/i3

The i3 binary you are running: /usr/bin/i3

- Linux Distribution & Version: Arch Linux

- Are you using a compositor (e.g., xcompmgr or compton): picom