Make libhidl_gtest_helper vendor_available. am: d17de9f5a5 am: 0c4a397d7e am: 2a0305dbee am: 522b7d9549

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

Change-Id: I6ffa0b433e0c7a2f73acf5bfe19d8d1988abfb11
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>