MDL-78860 qtype_calculatedmulti: PHP 8.2 compatibility

PHP 8.2 has deprecated setting properties on objects dynamically.
The qtype_calculatedmulti question type had two properties being
set this way($correctanswerlength and$correctanswerformat).
This patch extends the question_answer class to add the properties
when the object is instantiated.

question/type/calculatedmulti/classes/qtype_calculatedmulti_answer.php

@@ -0,0 +1,38 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle 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.
+//
+// Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace qtype_calculatedmulti;
+
+defined('MOODLE_INTERNAL') || die();
+
+require_once($CFG->dirroot . '/question/type/questionbase.php');
+
+/**
+ * Class to represent a calculated question answer.
+ *
+ * @package   qtype_calculatedmulti
+ * @copyright 2023 Matt Porritt <[email protected]>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class qtype_calculatedmulti_answer extends \question_answer {
+    /** @var int The length of the correct answer. */
+    public $correctanswerlength;
+
+    /** @var int The format of the correct answer. */
+    public $correctanswerformat;
+}

question/type/calculatedmulti/questiontype.php

@@ -23,6 +23,7 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+use qtype_calculatedmulti\qtype_calculatedmulti_answer;
 
 defined('MOODLE_INTERNAL') || die();
 
@@ -212,7 +213,8 @@ protected function initialise_question_instance(question_definition $question, $
      * @return question_answer
      */
     public function make_answer($answer) {
-        return parent::make_answer($answer);
+        return new qtype_calculatedmulti_answer($answer->id, $answer->answer,
+                $answer->fraction, $answer->feedback, $answer->feedbackformat);
     }
 
     protected function make_hint($hint) {