SF: Decouple MessageQueue

Define an ICompositor interface against which MessageQueue (which ought
to be an implementation detail of Scheduler) is implemented. Change the
equivocal invalidate/refresh nomenclature to commit/composite. Schedule
sampling only after composite.

Bug: 185535769
Test: libsurfaceflinger_unittest
Change-Id: I0c18f312459bae48531449f24f7b53c104fc5812
diff --git a/services/surfaceflinger/RegionSamplingThread.cpp b/services/surfaceflinger/RegionSamplingThread.cpp
index aa2fec5..9465b19 100644
--- a/services/surfaceflinger/RegionSamplingThread.cpp
+++ b/services/surfaceflinger/RegionSamplingThread.cpp
@@ -150,7 +150,7 @@
     if (mSampleRequestTime.has_value()) {
         ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForSamplePhase));
         mSampleRequestTime.reset();
-        mFlinger.scheduleRegionSamplingThread();
+        mFlinger.scheduleSample();
     }
 }