SurfaceFlingerPerfTests: Reduce variability in results

- use custom interation counter since simpleperf is run over entire test
- move all setup to @Before so its not recorded by simpleperf
- make test activity fullscreen to remove buffer updates from statusbar

Bug: 230039226
Test: atest SurfaceFlingerPerfTest

Change-Id: Id8c03b4dd32c012f091ab602fff780308420742f
Merged-In: Id8c03b4dd32c012f091ab602fff780308420742f