Limit AbortSignal.timeout to Window and Worker

Worklets are designed with minimal event loops such that they need only run a single task and corresponding microtasks, making APIs that schedule additional tasks unsuitable for worklets. As such, we restrict the availability of AbortSignal.timeout to Window and Worker since the API schedules a task to implement the timeout.

Closes #1054.

Author: shaseley

dom.bs

@@ -1771,7 +1771,7 @@ to <a for=AbortSignal>signal abort</a> on <a>this</a>'s <a for=AbortController>s
 [Exposed=*]
 interface AbortSignal : EventTarget {
   [NewObject] static AbortSignal abort(optional any reason);
-  [NewObject] static AbortSignal timeout([EnforceRange] unsigned long long milliseconds);
+  [Exposed=(Window,Worker), NewObject] static AbortSignal timeout([EnforceRange] unsigned long long milliseconds);
 
   readonly attribute boolean aborted;
   readonly attribute any reason;