Update interfaces/worklets.idl (#18578)

Source: https://github.com/tidoust/reffy-reports/blob/388ffc9/whatwg/idl/worklets.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/574704041

Author: autofoolip

interfaces/worklets.idl

@@ -7,6 +7,7 @@
 interface WorkletGlobalScope {
 };
 
+[Exposed=Window]
 interface Worklet {
     [NewObject] Promise<void> addModule(USVString moduleURL, optional WorkletOptions options);
 };