Enhance iOS export

- The export process now builds complete .ipa on macOS, instead of just
   creating XCode project.

 - The project includes Capabilities games usually require: Game Center,
   Push Notifications, In-App Purchase.

 - Icons and launch screens can be specified in export preset.

modules/gdnative/gdnative.cpp

@@ -234,8 +234,11 @@ bool GDNative::initialize() {
 		ERR_PRINT("No library set for this platform");
 		return false;
 	}
-
+#ifdef IPHONE_ENABLED
+	String path = lib_path.replace("res://", "dylibs/");
+#else
 	String path = ProjectSettings::get_singleton()->globalize_path(lib_path);
+#endif
 	Error err = OS::get_singleton()->open_dynamic_library(path, native_handle);
 	if (err != OK) {
 		return false;