Add system ui background handlers dispatch and delivery logging thresholds

Those thresholds would help us to further investigate bugs like this
one. Looper#showSlowLog prints Slog.w when the threshold is met. This risk free change will help us investigate issues when something got stuck in the background thread.

I've also removed misleading `run` from `UserTrackerImpl` because those are kotlin run to change context, which doesn't change execution thread.

Bug: 281851220
Test: manual
Change-Id: I127ec03e15f76295484e34b0ff0f3e7ad9ac9b88