Feature: #85607 - New ThumbnailViewHelper to render thumbnails deferred

See forge#85607


A new ViewHelper for the backend to render thumbnails deferred was introduced.

The \TYPO3\CMS\Backend\ViewHelpers\ThumbnailViewHelper extends the ImageViewHelper and generates the image tag with the special URI.

<be:thumbnail image="{file.resource}" width="{thumbnail.width}" height="{thumbnail.height}" />


Thumbnails do not block the rendering of a page, because the processing runs an extra http request.