SF: move VSyncTracker and VSyncDispatch ownership to Scheduler

This is a first change towards removing the old DispSync interface
for VSyncReactor. This change allows Scheduler to use VSyncTracker and
VSyncDispatch directly to schedule work-based vsync callback rather than
periodic, to get better control on scheduling app / sf vsync callbacks.

Test: adb shell /data/nativetest64/libsurfaceflinger_unittest/libsurfaceflinger_unittest
Change-Id: I81637bf458337b03489faa580a79afa05f47c6c8