Desktop apps can detect modifier keys held during startup

Desktop apps can detect which modifier keys were held while the application started, before user code runs. Four new read-only properties — Keyboard.StartupAltDown, Keyboard.StartupCommandDown, Keyboard.StartupControlDown, and Keyboard.StartupShiftDown — report an immutable snapshot of the modifier keys held when the desktop framework finishes initialising, just before the Objo VM begins executing user code. This enables launch-time "special mode" behaviour (for example safe mode or a preferences reset) as an alternative to command-line arguments. The values are captured exactly once for the first process start and remain unchanged for the application's lifetime.