ResyncCallback in getLatestVsyncEventData.

Without resyncing, getLatestVsyncEventData might have wrong refresh rate
compared to hardware. `getLatestVsyncEventData` is an alternate way
to get vsync information, instead of posting callbacks to Choreographer.

Choreographer only needs to resync when the main thread is hogged by an
application for more than the threshold (currently 750ms), and simulated
vsync is no longer accurate.

Bug: 205721584
Test: atest libsurfaceflinger_unittest
Change-Id: I32c69b0368365c860fa0eb75f932e283e05a1302