Auto merge of #23281 - josephhutch:StereoPannerNode, r=Manishearth

StereoPannerNode DOM

<!-- Please describe your changes on the following line: -->

This is the DOM implementation for StereoPannerNode. Backend implemented in https://github.com/servo/media/pull/243.

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- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -20306,7 +20306,7 @@
    "testharness"
   ],
   "mozilla/interfaces.html": [
-   "c7e1929c626007e2ef3cdf9f2276620aa995c5b7",
+   "2effd46f565c4787e8632f5e898e1b43d457672f",
    "testharness"
   ],
   "mozilla/interfaces.js": [

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

@@ -203,6 +203,7 @@ test_interfaces([
   "Response",
   "Screen",
   "ShadowRoot",
+  "StereoPannerNode",
   "Storage",
   "StorageEvent",
   "StyleSheet",