Update the Animation Worklet IDL file + test (#12444)

Copied from:
https://github.com/tidoust/reffy-reports/blob/f14a522/whatwg/idl/animation-worklet.idl

animation-worklet/idlharness.any.js

@@ -0,0 +1,17 @@
+// META: script=/resources/WebIDLParser.js
+// META: script=/resources/idlharness.js
+
+'use strict';
+
+// https://wicg.github.io/animation-worklet/
+
+idl_test(
+  ['animation-worklet'],
+  ['worklets', 'web-animations', 'html', 'cssom', 'dom'],
+  idl_array => {
+    idl_array.add_objects({
+      WorkletAnimation: ['new WorkletAnimation("name")'],
+      // TODO: WorkletGroupEffect
+    });
+  }
+);

interfaces/animation-worklet.idl

@@ -1,35 +1,31 @@
 // GENERATED CONTENT - DO NOT EDIT
-// Content of this file was automatically extracted from the
-// "CSS Animation Worklet API" spec.
-// See: https://wicg.github.io/animation-worklet/
+// Content was automatically extracted by Reffy into reffy-reports
+// (https://github.com/tidoust/reffy-reports)
+// Source: CSS Animation Worklet API (https://wicg.github.io/animation-worklet/)
 
-partial interface Window {
+partial namespace CSS {
     [SameObject] readonly attribute Worklet animationWorklet;
 };
 
-callback VoidFunction = void ();
-
 [ Exposed=AnimationWorklet, Global=AnimationWorklet ]
 interface AnimationWorkletGlobalScope : WorkletGlobalScope {
     void registerAnimator(DOMString name, VoidFunction animatorCtor);
 };
 
 [Constructor (DOMString animatorName,
-              optional (AnimationEffectReadOnly or sequence)? effects = null,
+              optional (AnimationEffect or sequence<AnimationEffect>)? effects = null,
               optional AnimationTimeline? timeline,
               optional any options)]
 interface WorkletAnimation : Animation {
         readonly attribute DOMString animatorName;
 };
 
-interface WorkletGroupEffectReadOnly :  GroupEffectReadOnly {};
-
-interface WorkletGroupEffect :  WorkletGroupEffectReadOnly {};
-WorkletGroupEffect implements AnimationEffectMutable;
-WorkletGroupEffect implements GroupEffectMutable;
+interface WorkletGroupEffect {
+  sequence<AnimationEffect> getChildren();
+};
 
 [Exposed=AnimationWorklet]
-partial interface AnimationEffectReadOnly {
+partial interface AnimationEffect {
     // Intended for use inside Animation Worklet scope to drive the effect.
     attribute double localTime;
 };