Function write_window_pointer_moved_messages_system 

pub fn write_window_pointer_moved_messages_system(
    cursor_moved_reader: EguiContextMessageReader<'_, '_, CursorMoved>,
    egui_input_message_writer: MessageWriter<'_, EguiInputEvent>,
    egui_contexts: Query<'_, '_, (&EguiContextSettings, &mut EguiContextPointerPosition), With<EguiContext>>,
)

Reads MouseButtonInput messages and wraps them into EguiInputEvent (only for window contexts).