[onizet]

• Refactor the DataUri parsing to use ReadOnlySpan and avoid excessive string allocation.
• DataUri now provide a break-circuit if the uri is not an image
• DataUri is no longer a public class
• Merge the parsing logic of HtmlAttributeCollection with SplitCompositeAttribute. This gives the robust escaping parsing (parenthesis and quote).
• HttpUtility is no longer needed and the code was referring to HTML4 which is largely outdated.