extracted wxWrapSizer in separate files and somewhat improved it (heavily modified patch 1876663)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53500 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/xrc/xh_sizer.h

@@ -47,6 +47,7 @@ private:
     wxSizer*  Handle_wxGridSizer();
     wxSizer*  Handle_wxFlexGridSizer();
     wxSizer*  Handle_wxGridBagSizer();
+    wxSizer*  Handle_wxWrapSizer();
 
     void SetGrowables(wxFlexGridSizer* fsizer, const wxChar* param, bool rows);
     wxGBPosition GetGBPos(const wxString& param);