Add tests to exercise ActivityStarter precondition failures.

This changelist adds tests which simulate various scenarios
encountered during the initial stages of starting an activity. They
ensure that the expected errors are returned under specified
conditions.

Bug: 64750076
Test: bit FrameworksServicesTests:com.android.server.am.ActivityStarterTests

Change-Id: I93fef3dce020fe03a8b2001b75a875980506a0dd