This is important to allow catching the context menu events from the
composite control children at the main window level using the main
window ID: previously, these events used the (typically auto-generated
internally) ID of the child window, which was an implementation detail
and prevented the code binding to these events using the ID of e.g.
wxListCtrl itself from working under the other platforms, where
wxListCtrl is a generic composite window, even if it worked under MSW,
where wxListCtrl is native.
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