Add FakeVp8Encoder, change FakeEncoder to use BitrateAllocator for simulcast. Change call_test to use VP8 payload name for simulcast tests. This is reland after fixes for broken perf tests. Original Reviewed-on: https://webrtc-review.googlesource.com/91861 Bug: none Change-Id: I6999a499408787be43a74a26a16b7826a0814a7b Reviewed-on: https://webrtc-review.googlesource.com/95182 Reviewed-by: Artem Titov <titovartem@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24383}