Dump ABI for libmediametrics

It's not an LLNDK library, but has # apex APIs which need to be kept
stable.

Bug: 138219814
Test: development/vndk/tools/header-checker/utils/create_reference_dumps.py -libs libmediametrics -ref-dump-dir prebuilts/abi-dumps/platform

Change-Id: I93b494c13a46817719002e0028f4f80f0a55d512