Whether the frontend is ready to be presented to the user.
Whether a frontend is ready can depend on whether dependent services are available, or whether the initial fragment of an initial panel is measured and laid out.
A system UI should attach the panels provided by this frontend regardless of this state. However, a system UI can decide to show a splash screen or a loading screen on top of these panels until isReady is set to
true. There is no guarantee however that a frontend won't have its panels presented to the user before setting this to
Note: Be careful when implementing this. If a frontend takes longer than a reasonable amount of time to get ready, a system UI may hang or take measures to recover such as restarting the frontend or the IVI system.