rework LatencyTracker for testing

Modify the VisibleForTesting methods of the LatencyTracker class to
improve the testibility. The class is modified to support overriding
callbacks when actions/outcomes are taken by LatencyTracker based on
its inputs.

Test classes using LatencyTracker can now verify:
1. When PerfettoTrigger has been triggered
2. When FrameworkStatsLog is written to

This CL fixes a bug where only the global enable flag is
checked when calling onActionStart and onActionEnd. It also
adds a new enabled check for when the public logAction API is called.

Test: atest LatencyTrackerTest
Bug: 269254242
Change-Id: I4f8d21bca4a9e52fb3875e88387b8c8641f64c94