make wxControlContainer accept focus depending on whether it has any focusable children when using native TAB navigation too but also allow to manually override this automatic detection; added wxWindow::SetCanFocus() to notify GTK+ about changed focus state

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45267 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/window.h

@@ -592,6 +592,9 @@ public:
     bool CanAcceptFocusFromKeyboard() const
         { return AcceptsFocusFromKeyboard() && CanAcceptFocus(); }
 
+        // call this when the return value of AcceptsFocus() changes
+    virtual void SetCanFocus(bool WXUNUSED(canFocus)) { }
+
         // navigates inside this window
     bool NavigateIn(int flags = wxNavigationKeyEvent::IsForward)
         { return DoNavigateIn(flags); }