VoE: apply new style guide on VoE interfaces and their implementations

Changes:
1. Ran clang-format on VoE interfaces and their implementations.
2. Replaced virtual with override in derived classes.

R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49239004

Cr-Commit-Position: refs/heads/master@{#9130}
39 files changed