Avoid blocking calls during simulcast transceiver creation

Previously, initializing simulcast transceivers required synchronous
calls to the worker thread to update encoding parameters after the
sender was created. This resulted in unnecessary BlockingCalls during
the SDP negotiation process.

This change refactors the creation pipeline for RtpTransceivers and
VideoRtpSenders to accept initial simulcast state—including layer status
and rejection flags—at construction. By determining the correct initial
encodings via CalculateInitialEncodings during initialization, the
sender starts in the correct state.

Consequently, the negotiation logic in sdp_offer_answer.cc no longer
needs to perform follow-up worker thread calls for newly created
transceivers. This improves performance by reducing thread
synchronization overhead during peer connection setup.

Bug: webrtc:42222804
Change-Id: I13407e9f800e2fe889a7f429782e62f7619f3637
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/463761
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47484}