Pull the Voice Activity Detector out from the AGC

This change generates bit-exact values when running through audioproc_f than before.

This change was originally uploaded here:
* https://codereview.webrtc.org/1181933002/
* https://codereview.webrtc.org/1177043017/

And reverted because of an ASAN problem in Chrome here:
* https://codereview.webrtc.org/1192863006/
* https://codereview.webrtc.org/1194963003/

TBR=andrew@webrtc.org

Review URL: https://codereview.webrtc.org/1212543002

Cr-Commit-Position: refs/heads/master@{#9505}
39 files changed