Prevent transceiver crash during SDP local rejection

Ensure that transceivers remain valid when handling locally rejected
media content during SDP updates. Previously, the transceiver was
std::move()ed out of the update vector prematurely, which could cause it
to be destroyed before associated worker tasks had finished executing.

Fixed: chromium:504194151
Change-Id: Id38ce125cbe83a4ea709adfd1951613642cafc8e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/466140
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47528}