Add wxComboBox::Popup() and Dismiss() to manually show or hide its popup.

Add implementations for wxMSW and wxGTK.

Closes #11506.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63242 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/combobox.h

@@ -47,6 +47,9 @@ public:
     virtual int GetSelection() const = 0;
     virtual void GetSelection(long *from, long *to) const = 0;
 
+    virtual void Popup() { wxFAIL_MSG( wxT("Not implemented") ); };
+    virtual void Dismiss() { wxFAIL_MSG( wxT("Not implemented") ); };
+
     // may return value different from GetSelection() when the combobox
     // dropdown is shown and the user selected, but not yet accepted, a value
     // different from the old one in it