Reland "New video encoder API."

This reverts commit 56e63097498d0ad6fe2eca779b7df173cc6a0fca.

Reason for revert: Preparing for reland

Original change's description:
> Revert "New video encoder API."
>
> This reverts commit 42f12d5183016060dcddc0b515a53294853559fe.
>
> Reason for revert: tests fails downstream
>
> Original change's description:
> > New video encoder API.
> >
> > Also initial implementation wrapping the libaom AV1 encoder.
> >
> > Note that for now this is intended for prototype purposes.
> >
> > Bug: none
> > Change-Id: Iac42ca4aecb6a204601c9f00bfb300e3eda3c4f4
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/306181
> > Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> > Commit-Queue: Philip Eliasson <philipel@webrtc.org>
> > Reviewed-by: Erik Språng <sprang@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#42108}
>
> Bug: none
> Change-Id: I927260353afb91df6c7650364baee4f13a098efd
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/347883
> Commit-Queue: Philip Eliasson <philipel@webrtc.org>
> Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
> Reviewed-by: Philip Eliasson <philipel@webrtc.org>
> Owners-Override: Philip Eliasson <philipel@webrtc.org>
> Auto-Submit: Danil Chapovalov <danilchap@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#42111}

Bug: none
Change-Id: Ib72ef5359ead697d27301e2ca2408e8b27165931
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/349001
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42172}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index e5ead5b..a7a2ada 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -815,6 +815,7 @@
     "numerics/moving_average.h",
     "numerics/moving_percentile_filter.h",
     "numerics/percentile_filter.h",
+    "numerics/rational.h",
     "numerics/running_statistics.h",
     "numerics/sequence_number_unwrapper.h",
     "numerics/sequence_number_util.h",