Fix navbar to home for All Apps.

It reuses the predictive back animation now. In addition, if All
Apps entered directly into the Search state (i.e. via QSB), the
back gesture now scales the whole panel to indicate it will close
and return to the home screen (as opposed to closing Search within
All Apps).

Demo: https://drive.google.com/file/d/1wpaZg3JaSxDMMc62uU-1miP9RaIO10EB/view?usp=drive_link&resourcekey=0-h8qKzuDguwIE2vUDr0H6lQ

Fix: 406523972
Flag: EXEMPT bugfix
Test: Manual
Change-Id: I470d67e03b2d8bbbaa39aea76c7dde639cff62f5

src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java

@@ -557,6 +557,13 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         return mIsSearching;
     }
 
+    /**
+     * @return {@code true} if back gesture should exit search rather than change launcher state.
+      */
+    public boolean shouldBackExitSearch() {
+        return isSearching();
+    }
+
     @Override
     public void onActivePageChanged(int currentActivePage) {
         if (mSearchTransitionController.isRunning()) {