[AUDIO_WORKLET] Add interactive hard-pan test NFC (#24942)

Built on #24931 (it touches the same file, but a rebase after merge will
fix this). This adds hard-panned audio files to test that the left and
right channels don't get flipped with any changes to the audio worklet
code (relevant for #24891, which changes how the copies are performed).
```
test/runner interactive.test_audio_worklet_hard_pans
```
The bass track is hard-left (with its right muted), drums are right.

Author: cwoffenden

test/test_interactive.py

@@ -336,6 +336,13 @@ def test_audio_worklet_params_mixing(self):
     shutil.copy(test_file('webaudio/audio_files/emscripten-bass.mp3'), 'audio_files/')
     self.btest_exit('webaudio/audioworklet_params_mixing.c', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS'])
 
+  # Mixing test above with hard-pans to verify left and right ordering
+  def test_audio_worklet_hard_pans(self):
+    os.mkdir('audio_files')
+    shutil.copy(test_file('webaudio/audio_files/emscripten-beat-right.mp3'), 'audio_files/emscripten-beat.mp3')
+    shutil.copy(test_file('webaudio/audio_files/emscripten-bass-left.mp3'), 'audio_files/emscripten-bass.mp3')
+    self.btest_exit('webaudio/audioworklet_params_mixing.c', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS'])
+
   # Tests an AudioWorklet with a growable heap
   def test_audio_worklet_memory_growth(self):
     os.mkdir('audio_files')