Improvement description

Issue
As a developer I can't introduce a custom HTML sanitizer for WYSIWYG content.

For example:

services:
    App\HtmlSanitizer\HtmlSanitizer:
        decorates: html_sanitizer.sanitizer.pimcore.wysiwyg_sanitizer

This will cause an issue because of the typehint - WYSIWYG HTML sanitizer can only be of Symfony\Component\HtmlSanitizer\HtmlSanitizer type:

• https://github.com/pimcore/pimcore/blob/12.x/models/Document/Editable/Wysiwyg.php#L28
• https://github.com/pimcore/pimcore/blob/12.x/models/DataObject/ClassDefinition/Data/Wysiwyg.php#L34

Can't solve this issue by extending the Symfony's class because it's marked as final: https://github.com/symfony/html-sanitizer/blob/7.3/HtmlSanitizer.php#L23