flutter: Fix Platform::name_calledFromC()

The return type needs to be ffi.Pointer<Utf8>, not String.
This has been fixed in dartagnan

src/flutter/generated/KDDockWidgets/dart/lib/src/Platform.dart

@@ -292,7 +292,7 @@ class Platform {
     }
 //tag=1037
     final result = dartInstance.name();
-    return result;
+    return result.toNativeUtf8();
   }
 //tag=1024