SF/CE: Clean up header dependencies and combine mocks

CompositionEngine has for a while had a weird dependency on SF
DisplayHardware sources, even though SF depends on CompositionEngine.

This made it impossible to share mocks, so a few were duplicated.

This MINIMALLY cleans things up, by creating filegroups for
libsurfaceflinger_backend_sources, and
libsurfaceflinger_backend_mock_sources, as well as cc_library_header
targets for both.

A more complete cleanup is left to the future, which would require
reorganizing the files.

Bug: None
Test: m surfaceflinger_service_fuzzer
Test: atest libcompositionengine_test libsurfaceflinger_unittest
Flag: EXEMPT refactor

Change-Id: I9d32d715b1a693093e59c8150203c0d941aa0fb2
diff --git a/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp b/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
index 48ebc32..3e0c390 100644
--- a/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
@@ -26,9 +26,8 @@
 #include <gtest/gtest.h>
 #include <renderengine/mock/RenderEngine.h>
 
-#include "MockHWComposer.h"
 #include "TimeStats/TimeStats.h"
-#include "gmock/gmock.h"
+#include "mock/DisplayHardware/MockHWComposer.h"
 
 using namespace com::android::graphics::surfaceflinger;