Feature: #71775 - HtmlParser allows srcset

See forge#71775


The \TYPO3\CMS\Core\Html\HtmlParser - most commonly used when rendering RTE fields in the frontend - now handles the srcset attribute.

A casual use case for this are responsive images:

    <source media="(max-width: 799px)" srcset="small-image.jpg">
    <source media="(min-width: 800px)" srcset="larger-image.jpg">


Using source tag with srcset attribute is allowed and srcset values are prefixed correctly.