Make libhidl_gtest_helper vendor_available. am: d17de9f5a5 am: bad2fe7568 am: c33821e9cb am: 0772f96dad

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/libhidl/+/18453726

Change-Id: I6546b8a2a1e066ef6fbd65ce2a6c07be0d3ff5cc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>