Feature request: support for `goto_split:<n>` where `<n>` is a split index

This would be lovely to have, and is supported by at least Kitty and iTerm:

- Kitty [first-window](https://sw.kovidgoyal.net/kitty/conf/#shortcut-kitty.First-window) - cmd+<n>
- iTerm (no docs) - cmd+<n>