MDL-85881 questions: Handle multi-byte names during migration

We were using strlen() instead of core_text::strlen() when checking the
length of a question bank name created during the migration. This meant
that multibyte strings were counted as being too long, even though they
were within the character limit.

question/classes/local/bank/question_bank_helper.php

@@ -582,7 +582,7 @@ class question_bank_helper {
             }
         }
 
-        if (strlen($bankname) > self::BANK_NAME_MAX_LENGTH) {
+        if (\core_text::strlen($bankname) > self::BANK_NAME_MAX_LENGTH) {
             throw new \coding_exception(
                 'The provided bankname is too long for the database field.',
                 'Use question_bank_helper::get_bank_name_string to get a suitably truncated name.',

question/tests/local/bank/question_bank_helper_test.php

@@ -280,6 +280,33 @@ final class question_bank_helper_test extends \advanced_testcase {
         );
     }
 
+    /**
+     * Create a default instance, passing a multibyte-character name.
+     *
+     * The name has more bytes than the max length, but is within the character limit as they are multibyte characters.
+     */
+    public function test_create_default_open_instance_with_multibyte_name(): void {
+        $this->resetAfterTest();
+        self::setAdminUser();
+
+        $coursename = '';
+        while (strlen($coursename) < question_bank_helper::BANK_NAME_MAX_LENGTH) {
+            $coursename .= '🙂';
+        }
+        $course = self::getDataGenerator()->create_course(['shortname' => '🙂']);
+        $bankname = get_string('defaultbank', 'core_question', ['coursename' => $coursename]);
+        $this->assertTrue(strlen($bankname) > question_bank_helper::BANK_NAME_MAX_LENGTH);
+        $this->assertTrue(\core_text::strlen($bankname) < question_bank_helper::BANK_NAME_MAX_LENGTH);
+
+        question_bank_helper::create_default_open_instance($course, $bankname);
+
+        $modinfo = get_fast_modinfo($course);
+        $cminfos = $modinfo->get_instances_of('qbank');
+        $this->assertCount(1, $cminfos);
+        $cminfo = reset($cminfos);
+        $this->assertEquals($bankname, $cminfo->get_name());
+    }
+
     /**
      * Assert that viewing a question bank logs the view for that user up to a maximum of 5 unique bank views.
      *