Move event generation code for multiple selection mode to common code

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53715 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/listbox.h

@@ -94,6 +94,11 @@ public:
     // returns the item number at a point or wxNOT_FOUND
     int HitTest(const wxPoint& point) const { return DoListHitTest(point); }
 
+    // For generating events in multiple and extended mode
+    wxArrayInt m_oldSelections;
+    void UpdateOldSelections();
+    void CalcAndSendEvent();
+
 protected:
     virtual void DoSetFirstItem(int n) = 0;