MDL-36580 backup: Apply the decrypt() method to lti "secrets"

mod/lti/backup/moodle2/restore_lti_stepslib.php

@@ -87,6 +87,11 @@ class restore_lti_activity_structure_step extends restore_activity_structure_ste
         // TODO: MDL-34161 - Fix restore to support course/site tools & submissions.
         $data->typeid = 0;
 
+        // Try to decrypt resourcekey and password. Null if not possible (DB default).
+        // Note these fields were originally encrypted on backup using {link @encrypted_final_element}.
+        $data->resourcekey = $this->decrypt($data->resourcekey);
+        $data->password = $this->decrypt($data->password);
+
         $newitemid = $DB->insert_record('lti', $data);
 
         // Immediately after inserting "activity" record, call this.