[CORE][COMPOSER] Move extlib packages with immediate composer correspondent to composer dependencies

This adds a composer.json for all dependencies that are available

vendor/ezyang/htmlpurifier/library/HTMLPurifier/Exception.php

@@ -0,0 +1,12 @@
+<?php
+
+/**
+ * Global exception class for HTML Purifier; any exceptions we throw
+ * are from here.
+ */
+class HTMLPurifier_Exception extends Exception
+{
+
+}
+
+// vim: et sw=4 sts=4