Add flag to AMS.startInstrumentation() to disable hidden API checks

Some tests need to use hidden APIs to check the internal state of
the framework. For those special use cases, we add a new flag to
ActivityManagerService.startInstrumentation that enables to start
instrumented processes without hidden API enforcement. Individual
test harnesses can change their Am command to request the exemption.

Bug: 64382372
Test: adb shell am instrument --no-hidden-api-checks <component>
      adb logcat | grep 'Accessing hidden'
Change-Id: I1d734a95423fae90dae63ff09d5f606495830905