Implement sending wxIconizeEvent in wxOSX.

Translate windowDid{Miniaturize,Deminiaturize} callbacks to calls to
SendIconizeEvent().

Closes #16718.

(this is a backport of 31e1387541 from master)

include/wx/osx/nonownedwnd.h

@@ -113,7 +113,9 @@ public:
     virtual void HandleResized( double timestampsec );
     virtual void HandleMoved( double timestampsec );
     virtual void HandleResizing( double timestampsec, wxRect* rect );
-    
+
+    void OSXHandleMiniaturize(double WXUNUSED(timestampsec), bool miniaturized);
+
     void WindowWasPainted();
 
     virtual bool Destroy();