SF: pass a render rate to VsyncTracker instead of a divisor

passing a divisor to VsyncTracker might result in the wrong frame
rate when the vsync period is changing. The Divisor was calculated in
VsyncReactor which calculates it based on the new period, and passed
to VsyncTracker which might still be learning the new period, hence
using the old period.

Bug: 267780202
Test: SF unit tests
Change-Id: Ibb632d4ae6621a6ac0c0123e78f4c4d75699bd9e