PHP 7.3 v2 Specialization (#1110)

* Added support for PHP 7.3 v2 Specialization
* Add builder dockerfile for PHP7
* Support mcrypt in PHP 7.3

examples/php7/multifile/handlers/FileReader.php

@@ -0,0 +1,16 @@
+<?php
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Log\LoggerInterface;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+function execute($context)
+{
+    /** @var ResponseInterface $response */
+    $response = $context["response"];
+    /** @var LoggerInterface $logger */
+    $logger = $context["logger"];
+    $response->getBody()->write(file_get_contents(__DIR__ . '/message.txt'));
+    $logger->debug('File read: example.txt');
+}