add themechange notify on win

Zhao Yuhang

2023-12-22 61cb997e4e9ebf50bcff835841fbd1ecc9499e49

 examples/mainwindow/mainwindow.h

@@ -28,6 +28,7 @@

private:
    void installWindowAgent();
    void installStyleAgent();
    void loadStyleSheet(Theme theme);

    Theme currentTheme{};