Add thread annotations to ChannelReceive members

payload_type_frequencies_ and payload_type_map_ are only accessed on the
worker thread, and rtp_ts_wraparound_handler_ and
capture_start_rtp_time_stamp_ only on the audio thread, but they are not
annotated. Annotate them so that the compiler checks the access rules.

Bug: webrtc:11993
Change-Id: I6ad5c753138891261ca6729d31e6904b1634ff5c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/506982
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Auto-Submit: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48794}