Set RtpVideoSender payload state in init list

The constructor default-initialized params_ and shared_frame_id_ and
then filled them in with a loop in its body. Compute both with helpers
in the initializer list instead. No behavior change.

Using `No-try` since the win_x86_more_configs bot keeps timing out.

Bug: webrtc:42223727
No-try: true
Change-Id: Id05861d0598acf54075d1235888255c54ac058b0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/506180
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48772}