MDL-69548 core: Adding the ZipStream library

This allows downloading of zip files as a stream, and will be used by
the Download course content project (MDL-69540).

lib/zipstream/src/Exception.php

@@ -0,0 +1,11 @@
+<?php
+declare(strict_types=1);
+
+namespace ZipStream;
+
+/**
+ * This class is only for inheriting
+ */
+abstract class Exception extends \Exception
+{
+}