Hooks for interracting with stage split components using legacy recentsanimation

Recents is pretty complicated, so the best way to deal with this is to
have launcher notify/query shell when entering recents. This gives
shell a chance to prepare and then provide relevant leashes (for now
just the bar, but it may include others in the future like side-
outline).

Bug: 192292305
Test: Enable SPLIT_SELECT and go to recents from split.
Change-Id: Iff6b14a1b0b95f207bdaa341c62fc6582659e923

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/ISplitScreen.aidl

@@ -90,4 +90,11 @@ interface ISplitScreen {
      oneway void startTasksWithLegacyTransition(int mainTaskId, in Bundle mainOptions,
                             int sideTaskId, in Bundle sideOptions, int sidePosition,
                             in RemoteAnimationAdapter adapter) = 11;
+
+    /**
+     * Blocking call that notifies and gets additional split-screen targets when entering
+     * recents (for example: the dividerBar).
+     * @param cancel is true if leaving recents back to split (eg. the gesture was cancelled).
+     */
+    RemoteAnimationTarget[] onGoingToRecentsLegacy(boolean cancel) = 12;
 }

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/SplitScreenController.java

@@ -40,6 +40,7 @@ import android.os.RemoteException;
 import android.os.UserHandle;
 import android.util.Slog;
 import android.view.RemoteAnimationAdapter;
+import android.view.RemoteAnimationTarget;
 import android.window.IRemoteTransition;
 
 import androidx.annotation.BinderThread;
@@ -267,6 +268,11 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
         return options;
     }
 
+    RemoteAnimationTarget[] onGoingToRecentsLegacy(boolean cancel) {
+        if (!isSplitScreenVisible()) return null;
+        return new RemoteAnimationTarget[]{mStageCoordinator.getDividerBarLegacyTarget()};
+    }
+
     public void dump(@NonNull PrintWriter pw, String prefix) {
         pw.println(prefix + TAG);
         if (mStageCoordinator != null) {
@@ -466,5 +472,14 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
                         controller.startIntent(intent, fillInIntent, stage, position, options);
                     });
         }
+
+        @Override
+        public RemoteAnimationTarget[] onGoingToRecentsLegacy(boolean cancel) {
+            final RemoteAnimationTarget[][] out = new RemoteAnimationTarget[][]{null};
+            executeRemoteCallWithTaskPermission(mController, "onGoingToRecentsLegacy",
+                    (controller) -> out[0] = controller.onGoingToRecentsLegacy(cancel),
+                    true /* blocking */);
+            return out[0];
+        }
     }
 }

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java

@@ -970,7 +970,7 @@ class StageCoordinator implements SplitLayout.SplitLayoutHandler,
         }
     }
 
-    private RemoteAnimationTarget getDividerBarLegacyTarget() {
+    RemoteAnimationTarget getDividerBarLegacyTarget() {
         final Rect bounds = mSplitLayout.getDividerBounds();
         return new RemoteAnimationTarget(-1 /* taskId */, -1 /* mode */,
                 mSplitLayout.getDividerLeash(), false /* isTranslucent */, null /* clipRect */,