Update channel constructors to support off-thread creation

Modify video and voice channel construction to remove operations that
bind to the construction thread. This is a step toward enabling channel
object creation on the signaling thread during negotiation without
needing to hop to the worker thread.

For voice channels:
* Initialize the `options_` member directly via the initializer list
  instead of calling `SetOptions` within the constructor body.
* This avoids redundant calls to `engine()->ApplyOptions` during
  construction.

For video channels:
* Remove the local `thread_checker_` from the send and receive channels.
* Use `worker_thread_` directly for thread safety annotations.
* Add explicit `thread_checker_` instances to the underlying stream
  classes where thread binding is still required.

Bug: webrtc:42222804
Change-Id: I5a37d08abc9e1311144a54a5b31a545bdb015d3d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/474980
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47809}