Only answer with non-stopped RTP header extensions

This extends the RTP header extension API usage to generating answers.

Also re-adds unit tests removed by the revert.

BUG=chromium:1051821

Change-Id: Ib754284e9a77cb49e22bea7072c475d240f2563b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298740
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#39800}
diff --git a/pc/media_session.h b/pc/media_session.h
index 6548f9c..87f04c7 100644
--- a/pc/media_session.h
+++ b/pc/media_session.h
@@ -285,7 +285,7 @@
       const SessionDescription* current_description,
       const TransportInfo* bundle_transport,
       const AudioCodecs& audio_codecs,
-      const RtpHeaderExtensions& default_audio_rtp_header_extensions,
+      const RtpHeaderExtensions& rtp_header_extensions,
       StreamParamsVec* current_streams,
       SessionDescription* answer,
       IceCredentialsIterator* ice_credentials) const;
@@ -299,7 +299,7 @@
       const SessionDescription* current_description,
       const TransportInfo* bundle_transport,
       const VideoCodecs& video_codecs,
-      const RtpHeaderExtensions& default_video_rtp_header_extensions,
+      const RtpHeaderExtensions& rtp_header_extensions,
       StreamParamsVec* current_streams,
       SessionDescription* answer,
       IceCredentialsIterator* ice_credentials) const;