Breaking: #67546 - Cleanup Flash message rendering in FlashMessageQueue 

See forge#67546

Description 

The rendering of flash messages has changed when using the view helper. Now the rendering output of TYPO3CMSCoreMessagingFlashMessageQueue::renderFlashMessages() is adapted to being exactly the same.

Impact 

Extensions using the rendered output of TYPO3CMSCoreMessagingFlashMessageQueue::renderFlashMessages() and in addition using HTML tags in flash messages for styling purposes will get their HTML flash message output properly HTML encoded. Thus the HTML tags will be visible in the rendered flash message output.

Since TYPO3CMSBackendTemplateDocumentTemplate also uses this rendering type, modules using this class will also be affected.

Affected Installations 

All extensions that use modules with TYPO3CMSBackendTemplateDocumentTemplate or are using TYPO3CMSCoreMessagingFlashMessageQueue::renderFlashMessages() directly.

Migration 

Remove all HTML from flash messages.