Add `navigate_command_palette` binding action

[mitchellh]

Add a new binding action navigate_command_palette which is an enum type which takes the values next and previous to start. This will move the selected item in the command palette forward and backward, respectively.

The design is based on navigate_search.

Replaces #7918

[jcollie]

I played with this a bit tonight and I don't think that this will work (on GTK at least) because when the command palette is showing GTK intercepts all key presses so that it can handle input in it's search field and it's own navigation keybinds. Ghostty itself never receives any key presses while the command palette is active.

The macOS command palette may handle key presses in a similar fashion.

[mitchellh]

macOS we can always add a responder on top of the other responders so we can always intercept input. We're also not using a native scroll list anyways in this case cause it can't really be customized to look proper. So it's not an issue.

With GTK, doesn't the work you did in your PR I closed work for this? (Just, a bit more dynamic since its based on config)

[jcollie]

Yes, my previous PR basically layered a custom event controller on top of the command palette and intercepted the key presses that I was interested in and passed everything else down back down to GTK. It wasn't configurable. Perhaps if a special keybind table named "command-palette" existed it could look in that table only for navigate_command_palette actions and intercept those and take action rather than using a hardcoded set of keys.