Avoid needless container and scoped_refptr copies

Several call sites deep-copy Codec, Candidate and logged RTP stream
objects, or whole vectors of them, that they only read. A few
constructors also copy by-value scoped_refptr parameters instead of
moving them.

- Bind getter results and loop elements by const reference: the codec
  lists in the SDP munging detector and in CodecList's AbslStringify,
  the port candidates in GetCandidateStatsFromReadyPorts, and the logged
  RTP streams in the NetEq event log input.
- Move by-value scoped_refptr parameters into their members in the
  PeerConnection, BroadcastResourceListener and
  ResourceVideoSendStreamForwarder constructors.

Bug: webrtc:374845009
Change-Id: I7f213313c894252896ccd3f39c03f455d5e84566
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/498621
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48805}