Add an ABI dump directory for libutils

The ABI dumps add visibility for API changes in a commonly used library.

Test: development/vndk/tools/header-checker/utils/create_reference_dumps.py \
      -libs libutils -products aosp_arm64 \
      -ref-dump-dir system/core/libutils/abi-dumps
Test: m libutils.vendor
Bug: 227282691
Change-Id: I498c62853562a8fc6702bdd622603b6f7d516274