Function write_keyboard_input_messages_system 

pub fn write_keyboard_input_messages_system(
    modifier_keys_state: Res<'_, ModifierKeysState>,
    keyboard_input_reader: EguiContextMessageReader<'_, '_, KeyboardInput>,
    egui_input_message_writer: MessageWriter<'_, EguiInputEvent>,
    egui_contexts: Query<'_, '_, &EguiContextSettings, With<EguiContext>>,
)

Reads KeyboardInput messages and wraps them into EguiInputEvent, can redirect messages to FocusedNonWindowEguiContext.