[FEATURE] Forward rendering context in VariablesViewHelper

It is now possible to use viewhelpers in emails, that require the
server request. For example the cObjectViewhelper.

Resolves: in2code-pro/powermail#94

Classes/ViewHelpers/Misc/VariablesViewHelper.php

@@ -59,6 +59,7 @@ public function render(): string
         $function = $this->arguments['function'];
         $mailRepository = GeneralUtility::makeInstance(MailRepository::class);
         $parseObject = GeneralUtility::makeInstance(StandaloneView::class);
+        $parseObject->setRenderingContext($this->renderingContext);
         $parseObject->setTemplateSource($this->removePowermailAllParagraphTagWrap($this->renderChildren()));
         $parseObject->assignMultiple(
             ArrayUtility::htmlspecialcharsOnArray($mailRepository->getVariablesWithMarkersFromMail($mail))