peerconnection_client sample on Windows is using the current UI thread as signaling thread. Create a dedicated thread for that purpose. Bug: webrtc:13104 Change-Id: Iccff8165373101996913c4389cf134a60051462c Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/230729 Reviewed-by: Per Kjellander <perkj@webrtc.org> Commit-Queue: Per Kjellander <perkj@webrtc.org> Cr-Commit-Position: refs/heads/main@{#35078}