update to v0.18.0

Original change: https://android-review.googlesource.com/c/platform/external/libgav1/+/2138217

This release includes 12-bit support and additions to DecoderBuffer to
support exposing Metadata OBUs.

changelog:
https://chromium.googlesource.com/codecs/libgav1/+log/v0.17.0..v0.18.0

Bug: b/230503757
Bug: b/227830772
Test: aosp_arm-eng aosp_arm64-eng aosp_x86-eng aosp_x86_64-eng
      aosp_barbet-userdebug compile
  aosp_oriole_hwasan-userdebug:
  - vts-tradefed run commandAndExit vts \
      --include-filter VtsHalMediaC2V1_0TargetVideoDecTest
      --module-arg "VtsHalMediaC2V1_0TargetVideoDecTest:include-filter:*av1*"
  - cts-tradefed run commandAndExit cts-dev \
    [ -a armeabi-v7a ] \
    --include-filter CtsMediaCodecTestCases \
    --module-arg "CtsMediaCodecTestCases:include-filter:.*(?i:av1)" \
    --include-filter CtsMediaDecoderTestCases \
    --module-arg "CtsMediaDecoderTestCases:include-filter:.*(?i:av1)" \
    --include-filter CtsMediaV2TestCases \
    --module-arg "CtsMediaV2TestCases:include-filter:.*(?i:av1)"
Change-Id: If0df9f11759fe158b2cc5745bc52ffff016d9753
Merged-In: I063fe55b802bf7f1bde202a84c31bca77d9efefd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
(cherry picked from commit d0cdd402efca9cb8485b3f66c1f665fe3ac976f8)