LibWeb: Port EventTarget to new {Fly}String

Author: https://github.com/kennethmyhra
Commit: 2091a11488
Pull-request: https://github.com/SerenityOS/serenity/pull/18255
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/DOM/EventTarget.idl

@@ -1,7 +1,7 @@
 #import <DOM/AbortSignal.idl>
 
 // https://dom.spec.whatwg.org/#eventtarget
-[Exposed=*]
+[Exposed=*, UseNewAKString]
 interface EventTarget {
 
     undefined addEventListener(DOMString type, EventListener? callback, optional (AddEventListenerOptions or boolean) options = {});