Implement wxComboBox::Popup() and Dismiss() for wxOSX/Cocoa.

Unlike in the other ports, these methods currently don't generate any events
under OS X because these events are never generated at all there.

Closes #12642.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69948 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/cocoa/private/textimpl.h

@@ -105,6 +105,9 @@ public :
     virtual wxString GetStringAtIndex(int pos) const;
 
     virtual int FindString(const wxString& text) const;
+    virtual void Popup();
+    virtual void Dismiss();
+
 private:
     NSComboBox* m_comboBox;
 };