cleanup the Win32 window classes registration code: remove global variables and register the window classes we use on demand to avoid registering MDI or GL classes unnecessarily

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57030 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/window.h

@@ -245,6 +245,9 @@ public:
     // get the HWND to be used as parent of this window with CreateWindow()
     virtual WXHWND MSWGetParent() const;
 
+    // get the Win32 window class name used by all wxWindow objects by default
+    static const wxChar *MSWGetRegisteredClassName();
+
     // creates the window of specified Windows class with given style, extended
     // style, title and geometry (default values
     //