win32: Use an invisible cursor when cursor-visible is FALSE

The win32 backend now handles the WM_SETCURSOR message and sets a
fully transparent cursor if the cursor-visible property has been
cleared on the stage. The icon is stored in the library via a resource
file. The instance handle for the DLL is needed to load the resource
so there is now a DllMain function to grab the handle.

clutter/win32/clutter-backend-win32.h

@@ -48,6 +48,8 @@ struct _ClutterBackendWin32
   HGLRC          gl_context;
   gboolean       no_event_retrieval;
 
+  HCURSOR        invisible_cursor;
+
   GSource       *event_source;
 };
 
@@ -68,6 +70,8 @@ clutter_backend_win32_add_options (ClutterBackend *backend,
 ClutterFeatureFlags
 clutter_backend_win32_get_features (ClutterBackend *backend);
 
+HCURSOR _clutter_backend_win32_get_invisible_cursor (ClutterBackend *backend);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_BACKEND_WIN32_H__ */