[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/extras/HTMLPurifierExtras.autoload-legacy.php

@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Legacy autoloader for systems lacking spl_autoload_register
+ *
+ * Must be separate to prevent deprecation warning on PHP 7.2
+ */
+
+function __autoload($class)
+{
+    return HTMLPurifierExtras::autoload($class);
+}
+
+// vim: et sw=4 sts=4