Add optional parameter to IVsyncSource::vsyncDeadlineAfter

vsyncDeadlineAfter just forwards its parameter to
VSyncTracker::nextAnticipatedVSyncTimeFrom, but the latter has an
optional parameter, too. Adding the optional parameter to
vsyncDeadlineAfter allows Scheduler::getNextFrameInterval to call it
directly. This will further help to move getNextFrameInterval's impl
into FrameTargeter::beginFrame, in
I229e09ccd760341268423fd4ba1ecc5105186f10.

Use Android's TimePoint and related classes directly in
getNextFrameInterval.

Bug: 315371484
Test: atest libscheduler_test:SchedulerTest#nextFrameIntervalTest
Change-Id: I1ede36d692b82a1f7276071fa558decced743334