Bootstrap email-editor unit tests

I also replaced using verify function by asserts, which will be removed in the higher version of phpunit.
[MAILPOET-6216]

packages/php/email-editor/tests/unit/_bootstrap.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types = 1);
+
+$console = new \Codeception\Lib\Console\Output([]);
+
+if (!function_exists('esc_attr')) {
+  function esc_attr($attr) {
+    return $attr;
+  }
+}
+
+abstract class MailPoetUnitTest extends \Codeception\TestCase\Test {
+  protected $runTestInSeparateProcess = false;
+  protected $preserveGlobalState = false;
+}
+
+include '_stubs.php';