an RTCRtpReceiver in which to install a position decoder.
a string used to identify this particular RTCRtpReceiver. When calling the
RemoteSourcePositionUpdate callback, this string will be passed as the first parameter.
When metadata is enabled, call setupReceiverMetadata to install decoders in RTCRtpReceivers. This will install either a RTCRtpScriptTransform (Safari) or use Insertable Streams (Chrome) to extract position information from transmitted audio data. When position information is extracted, the RemoteSourcePositionUpdate callback passed to setupHRTF will be called.