[TASK] Fix scroll behaviour of "Uncaught Exceptions" in backend

In the TYPO3 Backend of version 8, the iframe page (id
"typo3-contentIframe") is not scrollable, when an "uncaught exception" is
thrown and its content exceeds the page. The simplest way to fix this
behavior seems to be by adding 3 CSS rules to the very first div element
after the body tag in the iframe page (right, max-height and overflow;
"right" is needed to enable horizontal scrolling).

This solution is not perfect, when it comes to horizontal scrolling - but
better than the current situation.

Releases: 8.7
Resolves: #88096
Change-Id: I4ace93fc06fab48768944a5ef58958892ab51897
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60410
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Jonas Eberle
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Jonas Eberle
Reviewed-by: Simon Gilli <typo3@gilbertsoft.org>
Reviewed-by: Benni Mack <benni@typo3.org>

typo3/sysext/core/Classes/Error/DebugExceptionHandler.php

@@ -91,6 +91,9 @@ public function echoExceptionWeb(\Throwable $exception)
 							font-size: 12px;
 							margin: 10px;
 							padding: 0;
+							right: 10px;
+							overflow: scroll;
+							max-height: calc(100% - 24px);
 						">
 						<div style="width: 100%; background-color: #515151; color: white; padding: 2px; margin: 0 0 6px 0;">Uncaught TYPO3 Exception</div>
 						<div style="width: 100%; padding: 2px; margin: 0 0 6px 0;">