MDL-32188 quiz/question: behaviours can add to the review summary.

At the top of the quiz reivew page, there is a table that summarises
infomration about the quiz attempt as a whole. For some question
behaviours, we would like to be able to add additional information to
that summary.

This commit introduces a generic method for the behaviour to provide
summary information about an entire question usage.

question/engine/questionusage.php

@@ -326,6 +326,29 @@ class question_usage_by_activity {
         return $mark;
     }
 
+    /**
+     * Get summary information about this usage.
+     *
+     * Some behaviours may be able to provide interesting summary information
+     * about the attempt as a whole, and this method provides access to that data.
+     * To see how this works, try setting a quiz to one of the CBM behaviours,
+     * and then look at the extra information displayed at the top of the quiz
+     * review page once you have sumitted an attempt.
+     *
+     * In the return value, the array keys are identifiers of the form
+     * qbehaviour_behaviourname_meaningfullkey. For qbehaviour_deferredcbm_highsummary.
+     * The values are arrays with two items, title and content. Each of these
+     * will be either a string, or a renderable.
+     *
+     * @param question_display_options $options display options. Indicates what types
+     *      of information should, or should not, be returned.
+     * @return array as described above.
+     */
+    public function get_summary_information(question_display_options $options) {
+        return question_engine::get_behaviour_type($this->preferredbehaviour)
+                ->summarise_usage($this, $options);
+    }
+
     /**
      * @return string a simple textual summary of the question that was asked.
      */