Cleanup activity and task creation in unit tests.

This changelist replaces static methods used to create activity and
tasks with builders so that they can be extended in the future. This
change also removes the static default component names.

Bug: 64750076
Test: bit FrameworksServicesTests:com.android.server.am.ActivityRecordTests
Test: bit FrameworksServicesTests:com.android.server.am.ActivityStackSupervisorTests
Test: bit FrameworksServicesTests:com.android.server.am.ActivityStackTests
Test: bit FrameworksServicesTests:com.android.server.am.ActivityStarterTests
Test: bit FrameworksServicesTests:com.android.server.am.LaunchBoundsTests
Test: bit FrameworksServicesTests:com.android.server.am.LaunchingActivityPositionerTests
Test: bit FrameworksServicesTests:com.android.server.am.LaunchingTaskPositionerTests
Test: bit FrameworksServicesTests:com.android.server.am.LaunchingBoundsControllerTests
Test: runtest --path frameworks/base/services/tests/servicestests/src/com/android/server/am/RecentTasksTest.java
Change-Id: I389536b1dd618d4f80b5073ded7aeaacbab39cac