Auto merge of #21502 - Manishearth:listener, r=ferjm

Add AudioListener/AudioPanner DOM interfaces

Seems to work.

I'll need some changes to the servo-media side to support the panner
node getters as well as the older `setPosition()`/etc APIs. I'll get to
those later.

r? @ferjm

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -65286,7 +65286,7 @@
    "testharness"
   ],
   "mozilla/interfaces.html": [
-   "ad419477302c2f55fd0b0f7b90d4b36ee9700988",
+   "179f9c6c6928b3a4194c82f85cd1cce81123a5bc",
    "testharness"
   ],
   "mozilla/interfaces.js": [

tests/wpt/mozilla/tests/mozilla/interfaces.html

@@ -16,6 +16,7 @@ test_interfaces([
   "AudioBufferSourceNode",
   "AudioContext",
   "AudioDestinationNode",
+  "AudioListener",
   "AudioNode",
   "AudioParam",
   "AudioScheduledSourceNode",
@@ -173,6 +174,7 @@ test_interfaces([
   "OfflineAudioContext",
   "OscillatorNode",
   "PageTransitionEvent",
+  "PannerNode",
   "Performance",
   "PerformanceEntry",
   "PerformanceMark",