Add wxControlWithItems::SendSelectionChangedEvent() helper.

Reuse the same event generation code for wxChoice in wxMSW, wxGTK and wxOSX
and also wxComboBox in wxMSW and wxGTK instead of duplicating it (incompletely
and so partially incorrectly in wxOSX case).

This is just a refactoring so no changes in behaviour.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73102 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/ctrlsub.h

@@ -441,6 +441,12 @@ public:
     // colour
     virtual bool ShouldInheritColours() const { return false; }
 
+
+    // Implementation only from now on.
+
+    // Generate an event of the given type for the selection change.
+    void SendSelectionChangedEvent(wxEventType eventType);
+
 protected:
     // fill in the client object or data field of the event as appropriate
     //