Fix ext/dom object hierarchy

gen_stub.php references classes inside namespaces relatively

Author: kocsismate

ext/dom/php_dom.stub.php

@@ -607,7 +607,7 @@ public function isId(): bool {}
     }
 
     /** @alias DOM\Element */
-    class DOMElement extends DOMNode implements DOMParentNode, DOMChildNode
+    class DOMElement extends DOMNode implements \DOMParentNode, \DOMChildNode
     {
         /** @readonly */
         public string $tagName;
@@ -1032,7 +1032,7 @@ function dom_import_simplexml(object $node): DOMElement {}
      */
     const HTML_NO_DEFAULT_NS = UNKNOWN;
 
-    abstract class Document extends DOMNode implements DOMParentNode
+    abstract class Document extends \DOMNode implements \DOMParentNode
     {
         /** @readonly */
         public ?DocumentType $doctype;
@@ -1134,7 +1134,7 @@ public function replaceChildren(...$nodes): void {}
     }
 
     /** @strict-properties */
-    final class HTMLDocument extends DOM\Document
+    final class HTMLDocument extends Document
     {
         private function __construct() {}
 
@@ -1156,7 +1156,7 @@ public function saveHTMLFile(string $filename): int|false {}
     }
 
     /** @strict-properties */
-    final class XMLDocument extends DOM\Document
+    final class XMLDocument extends Document
     {
         /** @implementation-alias DOM\HTMLDocument::__construct */
         private function __construct() {}