Rename C++ API units to match new proto format units in metric.proto Bug: b/246095034 Change-Id: Ice5d388a080c474f275ef597f98fac1bcb98cf49 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/276100 Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Artem Titov <titovartem@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38137}