Take void** client data in wxSingleChoiceDialog ctor and not char**.

The client data is supposed to be untyped, there is really no reason (other
than compatibility with C conventions of 40 years ago) to use char** here.
So don't do it and provide the versions taking "void**" keeping "char**" ones
for backwards compatibility only.

Also deprecate GetSelectionClientData() that returned char* and add a new
GetSelectionData() returning void* instead.

Closes #13876.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70514 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/html/helpwnd.cpp

@@ -813,7 +813,9 @@ void wxHtmlHelpWindow::DisplayIndexItem(const wxHtmlHelpMergedIndexItem *it)
         wxSingleChoiceDialog dlg(this,
                                  _("Please choose the page to display:"),
                                  _("Help Topics"),
-                                 arr, NULL, wxCHOICEDLG_STYLE & ~wxCENTRE);
+                                 arr,
+                                 (void**)NULL, // No client data
+                                 wxCHOICEDLG_STYLE & ~wxCENTRE);
         if (dlg.ShowModal() == wxID_OK)
         {
             m_HtmlWin->LoadPage(it->items[dlg.GetSelection()]->GetFullPath());