SF: Introduce mock::DisplaySurface

Test: Builds
Bug: 74827900
Change-Id: I8526e671a22a53b62dc629b1978bfaaf9103e5ad
(cherry picked from commit 3190e2dc907a9d07318f8d58dddeab620c566d12)
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index 4989651..7dd5baa 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -21,6 +21,7 @@
         ":libsurfaceflinger_sources",
         "DisplayTransactionTest.cpp",
         "MockComposer.cpp",
+        "MockDisplaySurface.cpp",
         "MockEventControlThread.cpp",
         "MockEventThread.cpp",
         "MockGraphicBufferConsumer.cpp",