SF: Setup CompositionEngine::Layer

Add a Layer class to CompositionEngine, and modify ColorLayer and
BufferLayer to create them.

Also sets up CompositionEngine::LayerFE as an interface to be
implemented by the SF Layer class.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683
Change-Id: I2ed83355e81f36954b034ec60dd1a24c631f4874
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 619964f..f49733b 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -2227,6 +2227,10 @@
     return mDrawingState.inputInfo.token != nullptr;
 }
 
+std::shared_ptr<compositionengine::Layer> Layer::getCompositionLayer() const {
+    return nullptr;
+}
+
 // ---------------------------------------------------------------------------
 
 }; // namespace android