SurfaceFlinger: Modify the meaning of composition strategy changes

Modify the meaning of composition strategy changes to count sf move in
and out of client composition. When this happens too frequently, sf
offset changes rapidly - may cause system jank.

Bug: 144526027
Test: adb shell dumpsys SurfaceFlinger --timestats -dump
Change-Id: Ia9281b6fd6afe13386e48c3077a24660a8c1a6e3