Add default Full Screen command

[hyuri]

What is the problem or limitation you are having?

Much like #796, the default Full Screen shortcut(s) is(are) missing. Toga does not send the app into Full Screen when the default platform keyboard shortcut for Full Screen is pressed. (tested on macOS)

On macOS, two shortcuts are available by default: Command + Control + F and Fn + F.
On Windows and Linux, it's F11.

Describe the solution you'd like

Make the default platform keyboard shortcut for Full Screen trigger Full Screen.

Describe alternatives you've considered

None

Additional context

No response

[freakboy3742]

Makes sense. We might need to wait until #2473 is finalised before it's possible to implement this, though.

The implementation on macOS would be a menu item View > Enter Full Screen with the shortcut (Fn + F). That menu item should change text to "Exit Full Screen" when you're in full screen mode.

I don't have access to my Windows and GTK boxes right now, so I can't confirm what an appropriate menu rendition on Windows or GTK would be.