Leave xmlhttprequest.php for backward compatibility

Re-adding xmlhttprequest.php for plugins.  However, plugins should
be updated to use the new REST API approach.

Fixes #22593

xmlhttprequest.php

@@ -0,0 +1,48 @@
+<?php
+# MantisBT - A PHP based bugtracking system
+
+# MantisBT 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 2 of the License, or
+# (at your option) any later version.
+#
+# MantisBT 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 MantisBT.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * WARNING: This approach for doing AJAX calls is now deprecated in favor of the
+ * new REST API.
+ *
+ * @package MantisBT
+ * @copyright Copyright 2000 - 2002  Kenzaburo Ito - kenito@300baud.org
+ * @copyright Copyright 2002  MantisBT Team - mantisbt-dev@lists.sourceforge.net
+ * @link http://www.mantisbt.org
+ *
+ * @uses core.php
+ * @uses authentication_api.php
+ * @uses gpc_api.php
+ * @uses logging_api.php
+ */
+
+require_once( 'core.php' );
+require_api( 'authentication_api.php' );
+require_api( 'gpc_api.php' );
+require_api( 'logging_api.php' );
+
+auth_ensure_user_authenticated();
+
+$f_entrypoint = gpc_get_string( 'entrypoint' );
+
+$t_function = 'xmlhttprequest_' . $f_entrypoint;
+if( function_exists( $t_function ) ) {
+	log_event( LOG_AJAX, 'Calling {' . $t_function . '}...' );
+	call_user_func( $t_function );
+} else {
+	log_event( LOG_AJAX, 'Unknown function for entry point = ' . $t_function );
+	echo 'unknown entry point';
+}