Feature: #71775 - HtmlParser allows srcset

See forge#71775

Description

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:

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

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