Reland "Fix definition of keyframes decoded statistics"

This is a reland of commit 0e37f5ebd44183d9fe5318d844235aae28fda86a
with backward compability added to allow downstream tests to migrate to the new signature.

Original change's description:
> Fix definition of keyframes decoded statistics
>
> which are defined to be measured after decoding, not before:
>   https://w3c.github.io/webrtc-stats/#dom-rtcinboundrtpstreamstats-keyframesdecoded
>
> BUG=webrtc:14728
>
> Change-Id: I0a83dde278e1ebe8acf787bdac729af369a1ecf8
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/315520
> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Commit-Queue: Philipp Hancke <phancke@microsoft.com>
> Reviewed-by: Henrik Boström <hbos@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#40545}

BUG=webrtc:14728

Change-Id: I4cf52bb22ba8244155b4fa8c367b9c0306a77590
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/316120
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40553}

video/video_stream_decoder2.cc

diff --git a/video/video_stream_decoder2.cc b/video/video_stream_decoder2.cc
index ba36d12..5640835 100644
--- a/video/video_stream_decoder2.cc
+++ b/video/video_stream_decoder2.cc
@@ -46,9 +46,10 @@
 int32_t VideoStreamDecoder::FrameToRender(VideoFrame& video_frame,
                                           absl::optional<uint8_t> qp,
                                           TimeDelta decode_time,
-                                          VideoContentType content_type) {
+                                          VideoContentType content_type,
+                                          VideoFrameType frame_type) {
   receive_stats_callback_->OnDecodedFrame(video_frame, qp, decode_time,
-                                          content_type);
+                                          content_type, frame_type);
   incoming_video_stream_->OnFrame(video_frame);
   return 0;
 }