Use new traversal function when order doesn't matter

The new traversal function just handles traversing children and ignores relative layers. It also doesn't care about the z order. We continue to use the traverseInZOrder functions
for cases when z order matters.

This optimization reduces total CPU time spent in SurfaceFlinger.
Total ~2% savings

The savings where measured sampling over a 20 second period while TouchLatency
bouncy ball app was running.

Baseline
https://pprof.corp.google.com/?id=2ec0b6ac8e24e1571a3173c763ecd7e1&focus=LayerVector%3A%3AtraverseInZOrder

Optimized
https://pprof.corp.google.com/?id=23596aeb3e9db163956dc621dd19d7a4&focus=LayerVector%3A%3Atraverse

Test: manual. checked that normal use on the phone did not have graphical corruptions.
Test: atest SurfaceFlinger_test libcompositionengine_test libsurfaceflinger_unittest
Test: go/wm-smoke

Port from ag/10112179

Change-Id: I60cc6b58efc0e95c5ccc204830a3d76d2e7633c7