Update interfaces/audio-output.idl and test (#24457)

Closes https://github.com/web-platform-tests/wpt/pull/24456

Co-authored-by: Philip Jägenstedt <philip@foolip.org>
diff --git a/audio-output/idlharness.https.window.js b/audio-output/idlharness.https.window.js
index c13b167..d7cdbd0 100644
--- a/audio-output/idlharness.https.window.js
+++ b/audio-output/idlharness.https.window.js
@@ -7,13 +7,14 @@
 
 idl_test(
   ['audio-output'],
-  ['html', 'dom'],
+  ['mediacapture-streams', 'html', 'dom'],
   idl_array => {
     self.audio = document.createElement('audio');
     self.video = document.createElement('video');
     idl_array.add_objects({
       HTMLAudioElement: ['audio'],
-      HTMLVideoElement: ['video']
+      HTMLVideoElement: ['video'],
+      MediaDevices: ['navigator.mediaDevices'],
     });
   }
 );
diff --git a/interfaces/audio-output.idl b/interfaces/audio-output.idl
index cf0f46d..2041e6e 100644
--- a/interfaces/audio-output.idl
+++ b/interfaces/audio-output.idl
@@ -7,3 +7,7 @@
   [SecureContext] readonly attribute DOMString sinkId;
   [SecureContext] Promise<void> setSinkId (DOMString sinkId);
 };
+
+partial interface MediaDevices {
+  Promise<MediaDeviceInfo> selectAudioOutput();
+};