Function write_window_touch_messages_system 

pub fn write_window_touch_messages_system(
    commands: Commands<'_, '_>,
    egui_global_settings: Res<'_, EguiGlobalSettings>,
    modifier_keys_state: Res<'_, ModifierKeysState>,
    touch_input_reader: EguiContextMessageReader<'_, '_, TouchInput>,
    egui_input_message_writer: MessageWriter<'_, EguiInputEvent>,
    egui_contexts: Query<'_, '_, (&EguiContextSettings, &mut EguiContextPointerPosition, &mut EguiContextPointerTouchId, &EguiOutput), With<EguiContext>>,
)

Reads TouchInput messages and wraps them into EguiInputEvent.