SF: Move some Scheduler APIs to VsyncSchedule

Scheduler::getDisplayStatInfo forces callers to query both the deadline
and period, so split it into two VsyncSchedule APIs. Inline Scheduler::
getPreviousVsyncFrom.

Introduce <scheduler/Time.h> for type-safe, self-documenting wrappers
around std::chrono, which will gradually supersede nsecs_t (including
<scheduler/Fps.h> integration).

Clean up SF helpers for previous present fences. Remove the unnecessary
and inaccurate CompositorTiming initialization.

Bug: 185535769
Test: Perfetto timeline is green.
Change-Id: I22d8ad44ae37612e66f9d98fd4e7e1831951eb99