Skip Sender/Receiver hop for transferred Video Encoded frame transforms

Video equivalent of crrev.com/c/5638096.

After transferring Encoded Video Frame transform streams eg to a
worker, register the new underlying source as the TransformCallback,
rather than resolving a weak pointer to the
RTCRtpSender/RTCRtpReceiver and calling a method there, just to be
sent straight to the new underlying source.

This fixes the issue seen in crbug.com/347686125 for these transforms
of GC in an unrelated worker thread blocking the weak pointer
resolution, delaying video frames.

Bug: 347915599
Change-Id: Ieaad9d51434443a308bb278d707b5002cdafcc55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5648199
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Tony Herre <toprice@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1318616}