Improve inter-document focus handling (#36649)

*Describe the changes that this pull request makes here. This will be
the commit message.*
rewritten the PR #28571
Implement
[Window#focus](https://html.spec.whatwg.org/multipage/#dom-window-focus),
[Window#blur](https://html.spec.whatwg.org/multipage/#dom-window-blur)
Testing: WPT
Fixes: #8981 #9421

---------

Signed-off-by: kongbai1996 <1782765876@qq.com>
Co-authored-by: yvt <i@yvt.jp>

components/script/messaging.rs

@@ -72,6 +72,8 @@ impl MixedMessage {
                 ScriptThreadMessage::UpdateHistoryState(id, ..) => Some(*id),
                 ScriptThreadMessage::RemoveHistoryStates(id, ..) => Some(*id),
                 ScriptThreadMessage::FocusIFrame(id, ..) => Some(*id),
+                ScriptThreadMessage::FocusDocument(id, ..) => Some(*id),
+                ScriptThreadMessage::Unfocus(id, ..) => Some(*id),
                 ScriptThreadMessage::WebDriverScriptCommand(id, ..) => Some(*id),
                 ScriptThreadMessage::TickAllAnimations(..) => None,
                 ScriptThreadMessage::WebFontLoaded(id, ..) => Some(*id),