Route prepared file saves through platform services

src/platform_api/platform_services.h

@@ -8,6 +8,7 @@
 namespace pp::platform {
 
 using PickedPathCallback = std::function<void(std::string path)>;
+using PreparedFileCallback = std::function<void(std::string path, bool saved)>;
 
 class PlatformServices {
 public:
@@ -23,6 +24,10 @@ public:
     virtual void pick_file(std::vector<std::string> file_types, PickedPathCallback callback) = 0;
     virtual void pick_save_file(std::vector<std::string> file_types, PickedPathCallback callback) = 0;
     virtual void pick_directory(PickedPathCallback callback) = 0;
+    virtual void save_prepared_file(
+        std::string_view path,
+        std::string_view suggested_name,
+        PreparedFileCallback callback) = 0;
 };
 
 }