Add traces to aid onScreenTuringOn latency debugging

Those traces are useful to debug what happens in the unfold scenario: we discovered that recent changes added a lot of delay in systemui receiving onScreenTuringOn, and onDisplayChanged callbacks.

Bug: 197515205
Test: recorded a perfetto trace and made sure those are there
Change-Id: Iec9f2261dd63d414e1e5387933b7374a5f003e11