insertable streams: expose payload type

exposes the payload type in the encoded audio/video frame metadata
spec PR:
  w3c/webrtc-encoded-transform#117

BUG=webrtc:13077

Change-Id: I17340aec0b18637d7c1f3222add496a8aeb346ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3118568
Reviewed-by: Harald Alvestrand <[email protected]>
Reviewed-by: Tony Herre <[email protected]>
Commit-Queue: Philipp Hancke <[email protected]>
Cr-Commit-Position: refs/heads/main@{#918748}

Author: fippo

webrtc-encoded-transform/RTCPeerConnection-insertable-streams.js

@@ -27,6 +27,7 @@ function areArraysEqual(a1, a2) {
 
 function areMetadataEqual(metadata1, metadata2, type) {
   return metadata1.synchronizationSource === metadata2.synchronizationSource &&
+         metadata1.payloadType == metadata2.payloadType &&
          areArraysEqual(metadata1.contributingSources, metadata2.contributingSources) &&
          metadata1.frameId === metadata2.frameId &&
          areArraysEqual(metadata1.dependencies, metadata2.dependencies) &&