MDL-79876 qtype_ordering: Create an abstract class for the renderables

Part of: MDL-79863
Creates an abstract class in qtype_ordering/output that implements the
renderable interface. Each renderable that is used to output a given
component of the ordering question should extend this abstract class.

question/type/ordering/classes/output/renderable_base.php

@@ -0,0 +1,43 @@
+<?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/>.
+
+namespace qtype_ordering\output;
+
+use templatable;
+use renderable;
+use question_attempt;
+
+/**
+ * The base class for the renderables that are used to output the components of the ordering question.
+ *
+ * @package    qtype_ordering
+ * @copyright  2023 Mihail Geshoski <mihail@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+abstract class renderable_base implements templatable, renderable {
+
+    /** @var question_attempt $qa The question attempt object. */
+    protected $qa;
+
+    /**
+     * The class constructor.
+     *
+     * @param question_attempt $qa The question attempt object.
+     */
+    public function __construct(question_attempt $qa) {
+        $this->qa = $qa;
+    }
+}