Moar SystemServer boot timing improvements:

- Added (optional) constant to log duration of bottlenecks.
- Added TimingsTraceLog.getUnifinishedTraces()
- Added more traceBegin() / traceEnd() statements
- Uses Truth on TimingsTraceLogTest
- Logs total boot duration

Test: manual verification
Test: atest FrameworksCoreTests:android.util.TimingsTraceLogTest

Bug: 133242016
Bug: 132466534

Change-Id: Ib9bb38d357e0d87a9b7da3456c97029a8b0342a3