Configurable sample rate for hidden API log events

To reduce log spam, we do not log all hidden API accesses. This CL allows
configuration of the sampling rate of the log events so it can be tweaked
later if necessary.

Test: m
Test: $ adb shell settings put global hidden_api_access_log_sampling_rate 100
Bug: 64382372
Bug: 77517571
Change-Id: Ibec5d3d93bac4308f96c8d3a7a36de6add967eae