LibWeb: Implement Event.composedPath

I originally implemented this as something to use the new sequence
wrapper, however, after having a look at uses with grep.app, it's used
often, for example:
- Bootstrap 5 Dropdowns
- Polymer
- Angular
- Closure

Userland/Libraries/LibWeb/DOM/Event.idl

@@ -6,6 +6,7 @@ interface Event {
     readonly attribute EventTarget? target;
     readonly attribute EventTarget? srcTarget;
     readonly attribute EventTarget? currentTarget;
+    sequence<EventTarget> composedPath();
 
     readonly attribute unsigned short eventPhase;