Add missing c_str() and similar calls to samples in STL build.

Don't rely on implicit conversion of wxString to char*/wxChar*, it doesn't
exist in STL build. Add explicit c_str(), wc_str() or t_str() calls.

Closes #14420.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71820 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/uiaction/uiaction.cpp

@@ -213,7 +213,7 @@ void MyFrame::OnSimulateText(wxCommandEvent& WXUNUSED(event))
 
     wxUIActionSimulator sim;
     m_text->SetFocus();
-    sim.Text(s_text);
+    sim.Text(s_text.c_str());
 }
 
 void MyFrame::OnButtonPressed(wxCommandEvent& WXUNUSED(event))