Add GPL license header to rapidxml.hpp

Added copyright and GPL license information to the top of QuickLook.Native32/rapidxml.hpp for compliance and clarity.

QuickLook.Native/QuickLook.Native32/rapidxml.hpp

@@ -1,3 +1,20 @@
+// Copyright © 2017-2025 QL-Win Contributors
+// 
+// This file is part of QuickLook program.
+// 
+// This program 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.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 #ifndef RAPIDXML_HPP_INCLUDED
 #define RAPIDXML_HPP_INCLUDED