Provide a task-dialog based wxMSW wxMessageDialog implementation.

Use the task dialog instead of the legacy message box for wxMessageDialog
implementation under wxMSW on recent (Vista and later) Windows versions.

As part of this change, remove wxMessageDialogWithCustomLabels and integrate
its functionality in wxMessageDialogBase itself as it's now used by all
platforms.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65348 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/msgdlgg.h

@@ -24,13 +24,19 @@ public:
     virtual int ShowModal();
 
 protected:
+    // Creates a message dialog taking any options that have been set after
+    // object creation into account such as custom labels.
+    void DoCreateMsgdialog();
+
     void OnYes(wxCommandEvent& event);
     void OnNo(wxCommandEvent& event);
     void OnCancel(wxCommandEvent& event);
 
-private:
-    void DoCreateMsgdialog();
+    // can be overridden to provide more contents to the dialog
+    virtual void AddMessageDialogCheckBox(wxSizer *WXUNUSED(sizer)) { }
+    virtual void AddMessageDialogDetails(wxSizer *WXUNUSED(sizer)) { }
 
+private:
     wxPoint m_pos;
     bool m_created;