SF: Add initial Planner infrastructure

Adds infrastructure for the SF Planner, which will support layer
caching/flattening and composition strategy prediction.

Bug: 158790260
Test: atest libcompositionengine_test libsurfaceflinger_unittest
Change-Id: I0d3027cea073fe25f269f3d5e83fe621dfbe7b2b
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 14bb5b7..eb760b9 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -723,7 +723,7 @@
     // Returns the bounds of the layer without any buffer scaling.
     FloatRect getBoundsPreScaling(const ui::Transform& bufferScaleTransform) const;
 
-    int32_t getSequence() const { return sequence; }
+    int32_t getSequence() const override { return sequence; }
 
     // For tracing.
     // TODO: Replace with raw buffer id from buffer metadata when that becomes available.