Bug 1884211 - Put AudioData behind the Web Codecs pref. r=webidl,emilio

An oversight in the initial landing in bug 1858958.

Differential Revision: https://phabricator.services.mozilla.com/D204230

dom/webidl/AudioData.webidl

@@ -9,7 +9,7 @@
 
 // [Serializable, Transferable] are implemented without adding attributes here,
 // but directly with {Read,Write}StructuredClone and Transfer/FromTransfered.
-[Exposed=(Window,DedicatedWorker)]
+[Exposed=(Window,DedicatedWorker), Pref="dom.media.webcodecs.enabled"]
 interface AudioData {
   [Throws]
   constructor(AudioDataInit init);