Add return animation functionality to TransitionAnimator.

Bug: 323863002
Flag: ACONFIG com.android.systemui.shared.return_animation_framework_library DISABLED
Test: Manually tested existing use cases with the flag on and off (same
behavior), added unit test

Change-Id: I391c6ae784871e17262649d0f17343ac87b6a6d4
diff --git a/packages/SystemUI/animation/Android.bp b/packages/SystemUI/animation/Android.bp
index 2268d16..dce2c65 100644
--- a/packages/SystemUI/animation/Android.bp
+++ b/packages/SystemUI/animation/Android.bp
@@ -48,6 +48,7 @@
         "SystemUIShaderLib",
         "WindowManager-Shell-shared",
         "animationlib",
+        "com_android_systemui_shared_flags_lib",
     ],
 
     manifest: "AndroidManifest.xml",