Add a buffer class to store speech probabilities and to estimate speech
activity. Follows the implementation of speech activity computation in
LoudnessHistogram but uses floats for computations.
Bug: webrtc:7494
Change-Id: I6ee72ec52919904ea4e1fbe51d61993aa7813c9f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/277801
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Commit-Queue: Hanna Silen <silen@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38309}
