libbinder_random_parcel: rand binder returns data

We now have a 'RandomBinder' which can return random
data. For now, this doesn't integrate with random_parcel.h
RandomParcelOptions. This is to reduce complexity and
validate this approach.

Two ideas with this:
- when we're fuzzing AIDL services, complicated random
  parcel objects will get passed in (this RandomBinder)
- when we build AIDL fuzzers, we can use 'getRandomBinder'
  in order to dependency inject random binders into a
  service. This way, we can fuzz them assuming the
  dependencies are malicious.

Bug: 241923341
Test: android.hardware.vibrator-service.example_fuzzer (check that
   this code actually contributes to coverage)

Change-Id: I118d5c8d7b643fbd77f3771816600f74894e7bab