Feature: #78477 - Refactoring of FlashMessage rendering

Description

The implementation of rendering FlashMessages in the core has been optimized. With forge#73698 a cleanup has been started to centralize the markup within the FlashMessage class.

A new class called FlashMessageRendererResolver has been introduced. This class detects the context and renders the given FlashMessages in the correct output format. It can handle any kind of output format. The following FlashMessageRendererResolver classes have been introduced:

• \TYPO3\CMS\Core\Messaging\Renderer\BootstrapRenderer (is used in backend context by default)
• \TYPO3\CMS\Core\Messaging\Renderer\ListRenderer (is used in frontend context by default)
• \TYPO3\CMS\Core\Messaging\Renderer\PlaintextRenderer (is used in CLI context by default)

All new rendering classes have to implement the \TYPO3\CMS\Core\Messaging\Renderer\FlashMessageRendererInterface interface.

Impact

The core has been modified to use the new FlashMessageRendererResolver. Any third party extension should use the provided FlashMessageViewHelper or the new FlashMessageRendererResolver class:

$out = GeneralUtility::makeInstance(FlashMessageRendererResolver::class)
   ->resolve()
   ->render($flashMessages);