Don't recurse in Node::GetRootNode (#35725)

* Don't recurse in Node::GetRootNode

This causes servo to crash when computing
the root of deeply nested shadow roots.

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Add test case

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

tests/wpt/mozilla/meta/MANIFEST.json

@@ -13496,14 +13496,14 @@
      ]
     ],
     "interfaces.https.html": [
-     "6c48986beea5c8aca4e54c6da0fb8f3b7a4390e0",
+     "81f4d942f94366d8f9ecf22cfc3e1e22fe4ab8f1",
      [
       null,
       {}
      ]
     ],
     "interfaces.worker.js": [
-     "4ac5c822dcc6fbb021050ac2ab2ba4d04452d945",
+     "06eb8d3ba2334951cb1e0f791527ba118d4f13ec",
      [
       "mozilla/interfaces.worker.html",
       {}
@@ -14337,6 +14337,15 @@
      ]
     ]
    },
+   "shadow-dom": {
+    "getrootnode-in-deeply-nested-shadow.html": [
+     "355cc270e6020f40176afac26c49a14a59b67169",
+     [
+      null,
+      {}
+     ]
+    ]
+   },
    "webxr": {
     "create_session.https.html": [
      "5b5d485b372bfffb22204bc162c9e182306395cb",