Look in multiple paths when searching for resource files of samples

When using an out of source build, the files are not in the default wxWidgets directories.
Also search in the current directory, parent directory and sample sub-directories.

Closes https://trac.wxwidgets.org/ticket/18118

samples/widgets/textctrl.cpp

@@ -913,6 +913,7 @@ void TextWidgetsPage::OnButtonLoad(wxCommandEvent& WXUNUSED(event))
     wxPathList pathlist;
     pathlist.Add(wxT("."));
     pathlist.Add(wxT(".."));
+    pathlist.Add(wxT("../widgets"));
     pathlist.Add(wxT("../../../samples/widgets"));
 
     wxString filename = pathlist.FindValidPath(wxT("textctrl.cpp"));