Refactor Windows message dialog implementation

Split MessageDialog implementation for Windows into separate Win32 and WinUI3 files, with conditional inclusion based on the WINUI3_ENABLED flag. Win32 uses MessageBoxW, while WinUI3 uses ContentDialog via Windows App SDK. Also, update WindowId generation to use IdAllocator for uniqueness and consistency, and fix WindowManager to use the new WindowId logic.

Author: lijy91

src/platform/windows/menu_windows.cpp

@@ -1,4 +1,5 @@
 #include <windows.h>
+#include <cmath>
 #include <cstring>
 #include <functional>
 #include <iostream>