[BUGFIX] Frontend shows HTML tags in messages

Hardcoded linebreak tags in StatusMessages were not resolved to
linebreaks, but included into the output.
Replacing the <br /> tags with the nl command using the nl2br
viewhelper on the message output solves the problem.

Releases: 6.2
Resolves: #49266
Change-Id: I07f6dd389df1ce3eedb2b2f957da91f14b8f566f
Reviewed-on: https://review.typo3.org/21551
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters

typo3/sysext/install/Classes/Controller/Action/Tool/TestSetup.php

@@ -245,7 +245,7 @@ class TestSetup extends Action\AbstractAction implements Action\ActionInterface
 			$message = $this->objectManager->get('TYPO3\\CMS\\Install\\Status\\InfoStatus');
 			$message->setTitle('Compressed gif');
 			$message->setMessage(
-				'Method used by compress: ' . $methodUsed . '<br />'
+				'Method used by compress: ' . $methodUsed . LF
 				. ' Previous filesize: ' . $previousSize . '. Current filesize:' . $compressedSize
 			);
 		} else {
@@ -464,8 +464,8 @@ class TestSetup extends Action\AbstractAction implements Action\ActionInterface
 				'\'niceText\' is a concept that tries to improve the antialiasing of the rendered type by'
 				. ' actually rendering the textstring in double size on a black/white mask, downscaling the mask'
 				. ' and masking the text onto the image through this mask. This involves'
-				. ' ImageMagick \'combine\'/\'composite\' and \'convert\'.'
-				. ' <br />If the image has another background color than the image above (eg. dark background'
+				. ' ImageMagick \'combine\'/\'composite\' and \'convert\'.' . LF
+				. ' If the image has another background color than the image above (eg. dark background'
 				. ' color with light text) then you will have to set TYPO3_CONF_VARS[GFX][im_imvMaskState]=1'
 			);
 			$testResults['niceText']['message'] = $message;

typo3/sysext/install/Resources/Private/Partials/Action/Common/StatusMessage.html

-<div class="typo3-message message-{message.severity}" >
+<div class="typo3-message message-{message.severity}">
 	<div class="header-container">
 		<div class="message-header message-left"><strong>{message.title}</strong></div>
 		<div class="message-header message-right"></div>
 	</div>
-	<div class="message-body">{message.message}</div>
+	<div class="message-body">
+		<f:format.nl2br>{message.message}</f:format.nl2br>
+	</div>
 </div>
 <p></p>
\ No newline at end of file