Adds the ability for Launcher3 to respond to QSB alpha change requests.

Test: Tested locally
BUG:124063782
Change-Id: I8c4bfaa62d9608fcfffff5e30b2913f3a6fb2f75
(cherry picked from commit 827f0807d3)

quickstep/recents_ui_overrides/src/com/android/quickstep/FallbackActivityControllerHelper.java

@@ -75,6 +75,11 @@ public final class FallbackActivityControllerHelper implements
         // TODO:
     }
 
+    @Override
+    public void onAssistantVisibilityChanged(float visibility) {
+        // TODO:
+    }
+
     @NonNull
     @Override
     public HomeAnimationFactory prepareHomeUI(RecentsActivity activity) {