refactor: Restructure file dialog handling and introduce utility classes

- Updated file dialog references across the application to utilize a new `util::FileDialogWrapper` for consistent file handling.
- Refactored existing code to replace direct calls to `core::FileDialogWrapper` with the new utility class, enhancing modularity and maintainability.
- Introduced `util::PlatformPaths` for cross-platform directory management, ensuring consistent access to user directories and application data paths.
- Added new utility functions for file operations, improving the overall file handling capabilities within the application.
- Updated CMake configurations to include new utility source files, streamlining the build process.

src/app/editor/sprite/sprite_editor.cc

@@ -1,7 +1,7 @@
 #include "sprite_editor.h"
 
 #include "app/gfx/performance_profiler.h"
-#include "app/core/platform/file_dialog.h"
+#include "util/file_util.h"
 #include "app/editor/sprite/zsprite.h"
 #include "app/gfx/arena.h"
 #include "app/gui/icons.h"
@@ -254,7 +254,7 @@ void SpriteEditor::DrawCustomSpritesMetadata() {
   // ZSprite Maker format open file dialog
   if (ImGui::Button("Open ZSprite")) {
     // Open ZSprite file
-    std::string file_path = core::FileDialogWrapper::ShowOpenFileDialog();
+    std::string file_path = util::FileDialogWrapper::ShowOpenFileDialog();
     if (!file_path.empty()) {
       zsprite::ZSprite zsprite;
       status_ = zsprite.Load(file_path);