Register iframes with the devtools (#35874)

Previously, the devtools didn't know about
<iframe>s. They either ignored messages coming from
iframes or crashed.

This reverts https://github.com/servo/servo/pull/34032
and then filters out non-tab globals in the "listTabs"
message to the root actor.

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

components/script/dom/worker.rs

@@ -204,6 +204,7 @@ impl WorkerMethods<crate::DomTypeHolder> for Worker {
                 let page_info = DevtoolsPageInfo {
                     title,
                     url: worker_url.clone(),
+                    is_top_level_global: false,
                 };
                 let _ = chan.send(ScriptToDevtoolsControlMsg::NewGlobal(
                     (browsing_context, pipeline_id, Some(worker_id)),