SurfaceFlinger: Add "Abstract" Layer type.

Add an Abstract Layer type which exists only to be a parent. We
will use this to more cleanly represent the various hierarchy Layers
from the WM and for an upcoming screenshot rework.

Bug: 72760590
Test: Existing tests pass
Change-Id: Icd19ab0a467585660a95ae37b9c5dd4b8106da9d
diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index 3531c4e..ecb5971 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -84,6 +84,7 @@
         "BufferLayerConsumer.cpp",
         "Client.cpp",
         "ColorLayer.cpp",
+        "ContainerLayer.cpp",
         "DisplayDevice.cpp",
         "DisplayHardware/ComposerHal.cpp",
         "DisplayHardware/FramebufferSurface.cpp",