[php-src] PR #23598: dom: register unprefixed id attributes from foreign content in HTML

Pull Request: https://github.com/php/php-src/pull/23598 Author: iliaal The HTML5 parser bridge only marked an id attribute as XML_ATTRIBUTE_ID when the attribute's lexbor namespace was LXB_NS_HTML, so ids on SVG and MathML elements never reached Dom\HTMLDocument::getElementById(). The condition the bridge wants is that the attribute is unprefixed, which lxml_attr->ns already records: the struct is memset to zero and ns is assigned only in the xmlns, xlink and xml branches above. Testing lxml_attr->ns == NULL covers every element namespace instead of an enumerated subset, and the test pins that a namespaced xml:id is still not registered.