webcodecs: Temporal SVC encode

1. Adding VideoEncoderConfig.scalabilityMode and EncodedVideoChunkMetadata
2. Connecting them to SVC fields in media::VideoEncoder config and output
3. Renaming VideoEncoderOutputCallback to EncodedVideoChunkOutputCallback
   in order to comply with the spec.
4. Deleting EncodedVideoMetadata, it doesn't do anything,
   and can be confused with EncodedVideoChunkMetadata
5. New test: temporal_svc.any.js

Bug: 1176474
Change-Id: Ia89ec093c55df4495f50d51262bcc75c578fd8d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2755947
Commit-Queue: Eugene Zemtsov <eugene@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#863171}

webcodecs/video-encoder.any.js

@@ -60,7 +60,10 @@ promise_test(t => {
 promise_test(async t => {
   let output_chunks = [];
   let codecInit = getDefaultCodecInit(t);
-  codecInit.output = chunk => output_chunks.push(chunk);
+  codecInit.output = (chunk, metadata) => {
+    assert_not_equals(metadata, null);
+    output_chunks.push(chunk);
+  }
 
   let encoder = new VideoEncoder(codecInit);
 
@@ -102,7 +105,7 @@ promise_test(async t => {
   let bitmap = await generateBitmap(320, 200);
   let encoder = null;
   let reset_completed = false;
-  codecInit.output = chunk => {
+  codecInit.output = (chunk, metadata) => {
     if (chunk.timestamp % 2 == 0) {
       // pre-reset frames have even timestamp
       callbacks_before_reset++;