UI: Convert multiview layout string profiles to int

This commit series changes the ini user configuration multiview layout
so that string values were converted to int. In order to prevent past
user saves to break we verify if the ini still have string values and
convert that to int on obs init.

This will make the code easier to maintain in clearer to read the
multiview layout settings, also, makes the addition of new layouts
easier.

UI/obs-app.hpp

@@ -78,6 +78,8 @@ private:
 
 	std::deque<obs_frontend_translate_ui_cb> translatorHooks;
 
+	bool UpdatePre22MultiviewLayout(const char *layout);
+
 	bool InitGlobalConfig();
 	bool InitGlobalConfigDefaults();
 	bool InitLocale();