MDL-85200 mod_quiz: Improve efficience of populate_question_sources

This uses the contexts from the categories of questions in the quiz to
narrow down the list of course modules we are querying to just those we
will need.

mod/quiz/classes/structure.php

@@ -1865,12 +1865,18 @@ class structure {
     private function populate_question_sources(): void {
         global $DB;
 
-        $sql = 'SELECT c.id AS contextid, cm.id, cm.course
-                  FROM {question_categories} qc
-                  JOIN {context} c ON c.id = qc.contextid
-                  JOIN {course_modules} cm ON cm.id = c.instanceid AND c.contextlevel = ' . CONTEXT_MODULE . '
-              GROUP BY c.id, cm.id, cm.course';
-        $this->questionsources = $DB->get_records_sql($sql);
+        $contextids = array_map(fn($question) => $question->contextid, $this->questions);
+        [$insql, $inparams] = $DB->get_in_or_equal(array_unique($contextids));
+
+        $sql = "
+            SELECT c.id as contextid, cm.id, cm.course
+              FROM {context} c
+              JOIN {course_modules} cm ON cm.id = c.instanceid AND c.contextlevel = ?
+             WHERE c.id {$insql}
+        ";
+        $params = array_merge([context_module::LEVEL], $inparams);
+
+        $this->questionsources = $DB->get_records_sql($sql, $params);
     }
 
     /**