Move libgav1-based Av1QpParser to modules/video_coding/utility.

This make the qp parser available to use in other tests than the
corruption detection ones, e.g. for the new encoder api. The target is
still restricted to `test_only`. Also slightly refactored the code
somewhat so that the libgav1 includes can be completely contained to
within the .cc file, preventing issues when other classes import the
parser header.

No-Presubmit: True
Bug: webrtc:496266459
Change-Id: Ief16e484a8929cdc1868a4beb5855b4380254dc1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/472220
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47756}