Initializes the CMouseManager object.
If you call CWinAppEx::GetMouseManager, the default implementation of that method calls InitMouseManager.
If your application already has a mouse manager and you call InitMouseManager, your application will have an ASSERT failure. Therefore you should not call InitMouseManager if you create a CMouseManager object directly. If you are not using a custom CMouseManager, you should use GetMouseManager to create a CMouseManager object.