Reland "Add a "deep parse" mode to Av1QpParser returning the true average QP."

This is a reland of commit 1c3123e3b40126235cc7b6531379bc6767dddb9a
Downstream build issue has been rectified.

Original change's description:
> Add a "deep parse" mode to Av1QpParser returning the true average QP.
>
> The normal AV1 QP parser just looks at the frame global QP specified in
> the frame header OBU. However, some implementation set a par macroblock
> offset relative to that global QP - so average may differ significantly.
>
> This CL introduces a more expensive mode where the full bitstream is
> parsed (but still no image data decoded), allowing the a true average
> QP to be calculated.
>
> Note that this is more computationally expensive and should only be
> used for testing and validation purposes.
>
> Bug: webrtc:496266459
> Change-Id: Ie62fb4d914f893ade412cf71b124d6c1f28760d0
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/474420
> Commit-Queue: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Philip Eliasson <philipel@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#47797}

Bug: webrtc:496266459
Change-Id: I8a1aab9f679457d7b9d5630141818444e706b3e7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/474742
Auto-Submit: Erik Språng <sprang@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47806}