Virtualize wxXmlNode methods used by wxAuiToolBarXmlHandler.

This fixes the DLL build of aui library as it can now be linked without
leaving any unresolved dependencies to the code in xml library (where
wxXmlNode is implemented).

Closes #15686.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75734 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/xrc/xmlres.h

@@ -481,6 +481,7 @@ public:
     // e.g. <object class="wxDialog">.
     bool IsOfClass(wxXmlNode *node, const wxString& classname) const;
 
+    bool IsObjectNode(const wxXmlNode *node) const;
     // Gets node content from wxXML_ENTITY_NODE
     // The problem is, <tag>content<tag> is represented as
     // wxXML_ENTITY_NODE name="tag", content=""
@@ -488,6 +489,10 @@ public:
     //        wxXML_CDATA_SECTION_NODE name="" content="content"
     wxString GetNodeContent(const wxXmlNode *node);
 
+    wxXmlNode *GetNodeParent(const wxXmlNode *node) const;
+    wxXmlNode *GetNodeNext(const wxXmlNode *node) const;
+    wxXmlNode *GetNodeChildren(const wxXmlNode *node) const;
+
     // Check to see if a parameter exists.
     bool HasParam(const wxString& param);