SF: add a work duration slack when missing a frame

When missing a frame, SF usually ends up waiting 1ms for the
previous fence to fire. This causes sometimes skipping the next frame
as the work duration with the 1ms pushes the vsync one more frame.

Bug: 354007767
Flag: com.android.graphics.surfaceflinger.flags.allow_n_vsyncs_in_targeter
Test: SF unit tests

Change-Id: Ia4e2791c420c17bcbe123bd61cc569695702a40c