Refactor get/set_property to take the item as first argument

lily/note-head-line-engraver.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 2000--2020 Jan Nieuwenhuizen <janneke@gnu.org>
 
   LilyPond is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
 
@@ skipping 50 matching lines @@
   last_staff_ = 0;
 }
 
 void
 Note_head_line_engraver::acknowledge_rhythmic_head (Grob_info info)
 {
   head_ = info.grob ();
   Context *tr = find_context_above (context (), ly_symbol2scm ("Staff"));
   if (tr
       && tr != last_staff_
-      && to_boolean (get_property ("followVoice")))
+      && to_boolean (get_property (this, "followVoice")))
     {
       if (last_head_)
         follow_ = true;
     }
   last_staff_ = tr;
 }
 
 void
 Note_head_line_engraver::process_acknowledged ()
 {
@@ skipping 38 matching lines @@
 
                 /* create */
                 "VoiceFollower ",
 
                 /* read */
                 "followVoice ",
 
                 /* write */
                 ""
                );