Fix setting layout direction for wxComboBox in wxMSW.

The EDIT control used by the native combobox is different from normal EDIT
controls and has to be handled specially.

We also need to explicitly forward WS_EX_LAYOUTRTL to the dropdown window as
it doesn't inherit it from the combobox itself automatically.

See #11583.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77754 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/combobox.h

@@ -126,6 +126,8 @@ public:
     virtual bool SetHint(const wxString& hint);
 #endif // wxUSE_UXTHEME
 
+    virtual void SetLayoutDirection(wxLayoutDirection dir) wxOVERRIDE;
+
 protected:
 #if wxUSE_TOOLTIPS
     virtual void DoSetToolTip(wxToolTip *tip);