[automerger skipped] external/libgav1: update to v0.16.3 am: 81461368d4 am: 948cd315d3 -s ours

am skip reason: skip tag Change-Id I87f41df0e6aa1bea210b43e4bff6487a9cb83269 with SHA-1 4da996f3f9 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/libgav1/+/14235244

Change-Id: I085f90a064bfcf2ad9c9f98c8c38c93a32830a03