Use createElementNS for namespaced XML elements (see #6157)

Description
-----------

~~WIP~~

See #6154

Using `createElement()` for namespaced elements is wrong, see https://dom.spec.whatwg.org/#ref-for-dom-document-createelement%E2%91%A0

Commits
-------

1951826 WIP
c13c331 WIP
b5c1220 WIP
323eec0 WIP
104ebc6 WIP
1b43c8b WIP
ea7434a WIP
5bce909 WIP
0a10c0c Fix namespaced elements
5521c56 Revert
27f5238 WIP
9e8604b WIP
109bf12 Fix

core-bundle/src/Controller/SitemapController.php

@@ -62,10 +62,10 @@ public function __invoke(Request $request): Response
         $urlSet = $sitemap->createElementNS('https://www.sitemaps.org/schemas/sitemap/0.9', 'urlset');
 
         foreach ($urls as $url) {
-            $loc = $sitemap->createElement('loc');
+            $loc = $sitemap->createElementNS($urlSet->namespaceURI, 'loc');
             $loc->appendChild($sitemap->createTextNode($url));
 
-            $urlEl = $sitemap->createElement('url');
+            $urlEl = $sitemap->createElementNS($urlSet->namespaceURI, 'url');
             $urlEl->appendChild($loc);
             $urlSet->appendChild($urlEl);
         }

core-bundle/src/Event/SitemapEvent.php

@@ -38,10 +38,10 @@ public function addUrlToDefaultUrlSet(string $url): self
             return $this;
         }
 
-        $loc = $sitemap->createElement('loc');
+        $loc = $sitemap->createElementNS($urlSet->namespaceURI, 'loc');
         $loc->appendChild($sitemap->createTextNode($url));
 
-        $urlEl = $sitemap->createElement('url');
+        $urlEl = $sitemap->createElementNS($urlSet->namespaceURI, 'url');
         $urlEl->appendChild($loc);
         $urlSet->appendChild($urlEl);