Add Composer autoloading functions and PHPStan for testing

vendor/nikic/php-parser/lib/PhpParser/ErrorHandler.php

@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser;
+
+interface ErrorHandler
+{
+    /**
+     * Handle an error generated during lexing, parsing or some other operation.
+     *
+     * @param Error $error The error that needs to be handled
+     */
+    public function handleError(Error $error);
+}