Reland "[metrics] Report not-idle to MetricsService in Ash on user activity"

This is a reland of commit c51d35fb70aa567ee6385ba9fb2ab8bb8b1f222f

There is no change from the original CL.

Reason for revert was addressed separately by crrev.com/c/5438673.

Original change's description:
> [metrics] Report not-idle to MetricsService in Ash on user activity
>
> Currently ChromeMetricsServiceClient reports user activity based on
> various browser action (page load, omnibox activity etc). With
> Lacros enabled out there is a risk that the service client in Ash
> will become idle and cease to report metrics (since these browser
> actions occur in the Lacros browser process and are not propagated
> to Ash).
>
> This CL updates ChromeMetricsServiceClient to notify not-idle in
> Ash when activity has been reported via the UserActivityDetector.
> This class will regularly notify observers when activity is used
> for similar purposes elsewhere (turning off display for e.g.).
>
> Bug: 299290024
> Change-Id: I2428dc2e69605939092a5be9faceb0caed44706d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5425977
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1284836}

Bug: 299290024
Change-Id: I3990e4d5d45856883d3ccfe7a9e00cd9fe45b1c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5445363
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1287446}