Route prepared file saves through platform services

src/app_dialogs.cpp

@@ -23,8 +23,6 @@
 #include "oculus_vr.h"
 #elif __WEB__
 void webgl_pick_file(std::function<void(std::string)> callback);
-void webgl_pick_file_save(const std::string& path, 
-    const std::string& name, std::function<void(bool)> callback);
 void webgl_sync();
 #endif
 
@@ -459,7 +457,7 @@ void App::dialog_export(std::string ext)
         //auto result = ovr_Media_ShareToFacebook("Sharing from PanoPainter on Oculus Quest", path.c_str(), ovrMediaContentType_Photo);
 #elif __WEB__
         ui_task([=]{
-            webgl_pick_file_save(target.path, target.suggested_name, [](bool success){ });
+            save_prepared_file(target.path, target.suggested_name, [](const std::string&, bool) { });
         });
 #endif
     });