Enhance CMake configuration and update dependencies

- Updated CMakeLists.txt to set policies for older submodules, improving compatibility with various CMake versions.
- Modified vcpkg.json to change the SDL2 dependency to a core variant and updated the builtin baseline to the latest version, ensuring better package management.
- Improved file dialog functionality in file_dialog.cc by adding conditional compilation for NFD support, providing fallback behavior when NFD is unavailable.

vcpkg.json

@@ -5,8 +5,7 @@
   "dependencies": [
     "zlib",
     "libpng",
-    "sdl2",
-    "abseil"
+    "sdl2[core]"
   ],
-  "builtin-baseline": "c8696863d371ab7f46e213d8f5ca923c4aef2a00"
+  "builtin-baseline": "2024.12.16"
 }