[EncodedTransform] Expose Rid in TransformableVideoFrameInterface

This will aid in the implementation of the generateKeyFrame method
of EncodedTransform and the rid RTCVideoFrameMetadata field on the Web.

Bug: chromium:399327934
Change-Id: I8e5e9ebc3bcf99f4c25fcd7178852f8f5ad9d72b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/413240
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Guido Urdaneta <guidou@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45802}