Video timing simulator: Implement stream metrics.

This change implements aggregation of per-frame metrics into per-stream
metrics. There is some custom aggregation implemented, but the
aggregation of most metrics is delegated to `SamplesStatsCounter`.

I also took the opportunity to make the handling of the sentinel values
(infinite timestamps and time deltas) more robust.

Bug: b/423646186
Change-Id: Ia40cc4308f9fabdd137a7ac032194fed6a6a6964
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/448901
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46894}