Also moves the LibvpxVp8Interface from codec/vp8 to codec/interface and drops vp8 from the name. Follow-up CLs will wire up actual usage in the new classes through the interface so that we can unit test them more easily. Bug: webrtc:12274 Change-Id: I95f66e90245d9320e5fc23cdc845fbeb2648b38b Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/196522 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#32816}