Make rct_windowclass strong type WindowClass

This already revealed some places where implicit conversions were done, including some where its use was nonsense (MouseInput.cpp).
The changes to the Intent class were necessary to keep things working, and this splits things up more neatly.

src/openrct2/object/ObjectManager.cpp

@@ -490,7 +490,7 @@ private:
 
         // HACK Scenery window will lose its tabs after changing the scenery group indexing
         //      for now just close it, but it will be better to later tell it to invalidate the tabs
-        window_close_by_class(WC_SCENERY);
+        window_close_by_class(WindowClass::Scenery);
     }
 
     ObjectEntryIndex GetPrimarySceneryGroupEntryIndex(Object* loadedObject)