Batch worker thread tasks in [Get]StopTransceiverProcedure

Refactor StopTransceiverProcedure and StopSendingAndReceiving to return
worker thread operations as invocable tasks instead of executing them
immediately via BlockingCall. This allows SdpOfferAnswerHandler to batch
operations with other worker thread tasks, reducing the number of
synchronous thread hops during SDP negotiation.

Key changes:
- Update RtpTransceiver to return worker thread tasks.
- Introduce ScopedOperationsBatcher in SdpOfferAnswerHandler to collect
  and execute tasks in a single worker thread block.
- Ensure StopInternal and StopStandard maintain the existing synchronous
  behavior when batching is not used.
- Remove unused parameters and update tests to accommodate the
  task-based workflow.

Bug: webrtc:42222804
Change-Id: Ib253d382ee46d3da17e3ce6324a77ed3d22b73dc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/448460
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46889}