SurfaceFlinger: add a sysprop to ignore present fences

Emulation platform doesn't have accurate present fences.
If VSR is using the the timestamp from these present fences,
then the calculated timeline is jittery and inaccurate.
This change adds a new sysprop,
debug.sf.vsync_reactor_ignore_present_fences, that indicates
VSR to ignore present fences and instead use the vsync callbacks
to calculate the timeline.

Bug: 163165662
Test: Running emulation and collecting systraces
Change-Id: I8785b36d805e08d2cb340e3c15aa2ce4003843db