Function gamepad_event_processing_system 

pub fn gamepad_event_processing_system(
    gamepads: Query<'_, '_, (&mut Gamepad, &GamepadSettings)>,
    raw_events: MessageReader<'_, '_, RawGamepadEvent>,
    processed_events: MessageWriter<'_, GamepadEvent>,
    processed_axis_events: MessageWriter<'_, GamepadAxisChangedEvent>,
    processed_digital_events: MessageWriter<'_, GamepadButtonStateChangedEvent>,
    processed_analog_events: MessageWriter<'_, GamepadButtonChangedEvent>,
)

Consumes RawGamepadEvent events, filters them using their GamepadSettings and if successful, updates the Gamepad and sends GamepadAxisChangedEvent, GamepadButtonStateChangedEvent, GamepadButtonChangedEvent events.