Move smoothing filter to common audio.

This will make the smoothing filter a basic tool that is going to be used by both voice engine and ANA.

BUG=webrtc:6443

Review-Url: https://codereview.webrtc.org/2484153002
Cr-Original-Commit-Position: refs/heads/master@{#15146}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a82395bf7cd15b7396456df06fe952ede8db0c39
12 files changed